Why States Won’t Give Nuclear Weapons to Terrorists
Why States Won’t Give
Nuclear Weapons to
Terrorists
Keir A. Lieber and
达里尔·G. 按
For the last two de-
你跌倒了, 我们. leaders have focused on the possibility of nuclear terrorism as a se-
rious threat to the United States. In the wake of the terrorist attacks of
九月 11, 2001, those fears grew even more acute. In his State of the Union
Address four months after the attacks, President George W. Bush warned a
worried nation that rogue states “could provide [weapons of mass destruc-
的] to terrorists, giving them the means to match their hatred.”1 Both Vice
President Dick Cheney and National Security Adviser Condoleezza Rice amp-
liªed the president’s warning in order to justify the war against Iraq. Accord-
ing to Rice, “Terrorists might acquire such weapons from [Saddam Hussein’s]
政权, to mount a future attack far beyond the scale of 9/11. This terrible
prospect could not be ignored or wished away.”2 Such fears continue to shape
policy debates today: 尤其, advocates of bombing Iran’s nuclear fa-
cilities often justify a strike based on the idea that Iran might give nu-
Keir A. Lieber is Associate Professor in the Edmund A. Walsh School of Foreign Service and the Department
of Government at Georgetown University. 达里尔·G. Press is Associate Professor of Government at
Dartmouth College.
The authors thank Daniel Byman, Gregory Koblentz, Jennifer Lind, James Wirtz, and participants
in the Institute on Global Conflict and Cooperation Nuclear Security D.C. Policy Series for helpful
comments on earlier drafts of this article. They are also grateful to Benjamin Chuchla, Kunal
Malkani, and Lauren Weiss for their valuable research assistance.
1. President George W. Bush warned, “States like [伊拉克], and their terrorist allies, constitute an axis
of evil, arming to threaten the peace of the world. By seeking weapons of mass destruction, 这些
regimes pose a grave and growing danger. They could provide these arms to terrorists, giving
them the means to match their hatred.” Bush, “State of the Union Address,” January 29, 2002. 看
also White House, The National Security Strategy of the United States of America (华盛顿, 华盛顿特区:
White House, 九月 2002), PP. 13–16.
2. Condoleezza Rice, speech given to the Chicago Council on Foreign Relations, 芝加哥, 伊利诺伊州,
十月 8, 2003. Rice repeatedly connected Iraq’s alleged pursuit of nuclear weapons with terror-
主义. She explained the case for war against Iraq by arguing, “The problem here is that there will al-
ways be some uncertainty about how quickly he [Saddam Hussein] can acquire nuclear weapons.
But we don’t want the smoking gun to be a mushroom cloud. . . . There is certainly evidence that
al-Qaida people have been in Iraq. There is certainly evidence that Saddam Hussein cavorts with
terrorists. . . . We know that he is acquiring weapons of mass destruction, that he has extreme ani-
mus against the United States.” Rice, interview by Wolf Blitzer, Late Edition with Wolf Blitzer, CNN,
九月 8, 2002. 相似地, in the lead-up to the invasion, Vice President Dick Cheney asked rhe-
历史地, “Where might these terrorists acquire weapons of mass destruction, 化学武器,
biological weapons, 核武器? And Saddam Hussein becomes a prime suspect in that re-
gard because of his past track record. . . . We know he’s trying once again to produce nuclear
weapons and we know that he has a long-standing relationship with various terrorist groups, 在-
cluding the al-Qaida organization.” Cheney, interview by Tim Russert, Meet the Press, NBC,
行进 16, 2003.
国际安全, 卷. 38, 不. 1 (夏天 2013), PP. 80–104, 土井:10.1162/ISEC_a_00127
© 2013 由哈佛大学和麻省理工学院的校长和研究员撰写.
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Why States Won’t Give Nuclear Weapons to Terrorists 81
clear weapons to terrorist groups.3 Even President Barack Obama, who as a
senator opposed the war against Iraq, declared, “The American people face no
greater or more urgent danger than a terrorist attack with a nuclear weapon.”4
For U.S. 领导者, the sum of all fears is that an enemy might give nuclear weap-
ons to terrorists. But are those fears well founded?
The concern that a nuclear-armed state might transfer weapons to terrorists
is part of the foundation of U.S. nonproliferation policy. Nonproliferation is
pursued for a variety of reasons, including the fear that new nuclear states will
use their weapons directly against adversaries, even in the face of a clear risk
of retaliation; lose control of their nuclear weapons or materials through re-
gime incompetence, 腐败, or instability; trigger regional proliferation
cascades among nervous neighbors; or be emboldened to use nuclear weapons
as a “shield” for undertaking aggressive diplomatic and military actions, 骗局-
ªdent that other states could thus be deterred from responding forcefully.5 The
concern that a state might transfer nuclear weapons to terrorists, 然而, 是
among the greatest of these worries, and to many analysts it is the most com-
pelling justiªcation for costly actions—including the use of military force—
aimed at preventing proliferation.
Despite the issue’s importance, the danger of deliberate nuclear weapons
transfer to terrorists remains understudied.6 Scholars have scrutinized many
3. Emblematic of this concern is Norman Podhoretz’s depiction of “the menacing shadow of an
Iran armed with nuclear weapons, and only too ready to put them into the hands of the terrorist
groups.” He continues, “Even if [President Mahmoud] Ahmadinejad did not yet have missiles
with a long enough range to hit the United States, he would certainly be able to unleash a wave of
nuclear terror against us. If he did, he would in all likelihood act through proxies, for whom he
would with characteristic brazenness disclaim any responsibility even if the weapons used by
the terrorists were to bear telltale markings identifying them as of Iranian origin.” Podhoretz, “这
Case for Bombing Iran,” Commentary, 六月 2007, PP. 17–23, at p. 19.
4. White House, The National Security Strategy of the United States (华盛顿, 华盛顿特区: White House,
可能 2010), p. 23. For the views of other U.S. 领导者, see also the 2004 和 2008 presidential candi-
dates’ statements by John Kerry, 乔治·W. 衬套, John McCain, and Barack Obama in Francis J.
Gavin, “Same As It Ever Was: Nuclear Alarmism, 增殖, and the Cold War,“ 国际的
安全, 卷. 34, 不. 3 (冬天 2009/10), PP. 7–37, at p. 7.
5. An additional potential consequence of proliferation is not emphasized in the literature or in
policymakers’ statements: that an adversary’s nuclear weapons will be used to stalemate U.S. 骗局-
ventional military power, and hence complicate the United States’ global national security strat-
egy. See Keir A. Lieber and Daryl G. 按, “The Nukes We Need: Preserving the American
Deterrent,“ 外交事务, 卷. 88, 不. 6 (十一月十二月 2009), PP. 39–51.
6. For an analysis focusing on Iran and arguing that the risk of deliberate transfer of chemical,
生物, or nuclear weapons to terrorists is low, see Daniel L. Byman, “Iran, 恐怖主义,
and Weapons of Mass Destruction,” Studies in Conºict and Terrorism, 卷. 31, 不. 3 (春天
2008), PP. 169–181. See also the discussion in Daniel L. Byman, “Do Counterproliferation and
Counterterrorism Go Together?” Political Science Quarterly, 卷. 122, 不. 1 (春天 2007), PP. 25–46.
For a more pessimistic assessment, see Richard A. Falkenrath, Robert D. 纽曼, and Bradley A.
Thayer, 编辑。, America’s Achilles’ Heel: 核, Biological, and Chemical Terrorism and Covert Attack
(剑桥, 大量的。: 与新闻界, 1998), which concludes that the risk of states using terrorists to de-
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国际安全 38:1 82
other proliferation concerns more extensively. Analysts have investigated the
deductive and empirical bases for claims that new nuclear states would be
deterrable;7 the likelihood that Iran, 尤其, would behave rationally and
avoid using nuclear weapons recklessly;8 and the risks of proliferation cas-
你跌倒了,9 “loose nukes,”10 and nuclear-armed states using their weapons as a
shield for aggression or blackmail.11 To the extent that analysts have debated
liver weapons of mass destruction is a signiªcant and growing threat to the United States. 也可以看看
迈克尔·A. 列维, Deterring State Sponsorship of Nuclear Terrorism (华盛顿, 华盛顿特区: Council on For-
eign Relations, 2008).
7. Scott D. Sagan and Kenneth N. 华尔兹, The Spread of Nuclear Weapons: A Debate Renewed (新的
约克: W.W. 诺顿, 2002); Kenneth N. 华尔兹, “Nuclear Myths and Political Realities,” American Po-
litical Science Review, 卷. 84, 不. 3 (九月 1990), PP. 731–745; Kenneth N. 华尔兹, The Spread of
Nuclear Weapons: More May Be Better, Adelphi Papers, 不. 171 (伦敦: International Institute for
Strategic Studies, 1981); and Robert Jervis, The Meaning of the Nuclear Revolution: Statecraft and the
Prospect of Nuclear Armageddon (伊萨卡岛, 纽约: 康奈尔大学出版社, 1989).
8. Kenneth N. 华尔兹, “Why Iran Should Get the Bomb: Nuclear Balancing Would Mean Stability,”
外交事务, 卷. 91, 不. 4 (七月八月 2012), PP. 2–5. Evidence suggests that the Iranian gov-
ernment’s leadership is “rational” in the sense that its leaders are goal oriented and do not seek
their own destruction in pursuit of religious or ideological goals. On how Iran’s postrevolution
leadership has modulated its behavior in response to costs and risks, see Brenda Shaffer, “The Is-
lamic Republic of Iran: Is It Really?” in Shaffer, 编辑。, The Limits of Culture: Islam and Foreign Policy
(剑桥, 大量的。: 与新闻界, 2006), PP. 219–239. See also Juan Cole, Engaging the Muslim World
(纽约: 帕尔格雷夫·麦克米伦, 2009), 小伙子. 6.
9. Empirically, evaluations ªnd that nuclear acquisition by one country barely increases the odds
that any of its neighbors or enemies will acquire nuclear weapons. See William C. Potter, 和
Gaukhar Mukhatzhanova, 编辑。, Forecasting Nuclear Proliferation in the 21st Century: The Role of The-
奥里, 卷. 1 (帕洛阿尔托, 加利福尼亚州。: 斯坦福大学出版社, 2010), especially Philipp C. Bleek, “Why Do
States Proliferate? Quantitative Analysis of the Exploration, 追求, and Acquisition of Nuclear
武器,” in ibid., 小伙子. 8. See also William C. Potter, with Gaukhar Mukhatzhanova, 编辑。, Fore-
casting Nuclear Proliferation in the 21st Century: A Comparative Perspective, 卷. 2 (帕洛阿尔托, 加利福尼亚州。:
斯坦福大学出版社, 2010); Moeed Yusuf, “Predicting Proliferation: The History of the Fu-
ture of Nuclear Weapons,” Brookings Institution Foreign Policy Paper Series, 不. 11 (华盛顿,
华盛顿特区: 布鲁金斯学会, 一月 2009); William C. Potter and Gaukhar Mukhatzhanova, “Di-
vining Nuclear Intentions: A Review Essay,” 国际安全, 卷. 33, 不. 1 (夏天 2008),
PP. 139–169; Jacques E.C. Hymans, Achieving Nuclear Ambitions: Scientists, Politicians, and Prolifera-
的 (纽约: 剑桥大学出版社, 2012); and Johan Bergenas, “The Nuclear Domino
Myth,” Snapshot, 外交事务, 八月 31, 2010, http://www.foreignaffairs.com/articles/66738/
johan-bergenas/the-nuclear-domino-myth. John Mueller takes “cascadological hysteria” to task in
Mueller, Atomic Obsession: Nuclear Alarmism from Hiroshima to Al-Qaeda (纽约: Oxford Univer-
城市出版社, 2010), PP. 90–95.
10. This hypothesis has been intensely debated. See John Mueller, “Think Again: 核
武器,“ 对外政策, 不. 177 (一月二月 2010), PP. 38–44; Micah Zenko and Michael
A. 科恩, “Clear and Present Safety,“ 外交事务, 卷. 91, 不. 2 (March/April 2012), PP. 79–93;
Kenneth N. Luongo, “Loose Nukes in New Neighborhoods: The Next Generation of Proliferation
Prevention,” Arms Control Today, 卷. 35, 不. 4 (可能 2009), PP. 6–14; Graham T. Allison, Owen R.
Coté Jr., 理查德·A. Falkenrath, and Steven E. 磨坊主, Avoiding Nuclear Anarchy: Containing the
Threat of Loose Russian Nuclear Weapons and Fissile Material (剑桥, 大量的。: 与新闻界, 1996);
Matthew Bunn, Securing the Bomb 2010: Securing All Nuclear Materials in Four Years (剑桥,
大量的。: Project on Managing the Atom, Belfer Center for Science and International Affairs, 哈佛
Kennedy School, 2010); Mueller, Atomic Obsession, PP. 165–168, 208–210, 238; Gary Milhollin,
“Can Terrorists Get the Bomb?” Commentary, 二月 2002, PP. 45–49; and Karl-Heinz Kamp,
“An Overrated Nightmare,” Bulletin of the Atomic Scientists, 卷. 52, 不. 4 (七月八月 1996),
PP. 30–34.
11. See Todd S. Sechser and Matthew Fuhrmann, “Crisis Bargaining and Nuclear Blackmail,” In-
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Why States Won’t Give Nuclear Weapons to Terrorists 83
the possibility of covert state sponsorship of nuclear terrorism, 然而, 这
arguments have consisted mostly of competing deductive logics—with little
empirical analysis.
This article assesses the risk that states would give nuclear weapons to ter-
罗斯特. We examine the logical and empirical basis of the core proposition: 那
a state could surreptitiously transfer a nuclear weapon to a like-minded terror
团体, thus providing the means for a devastating attack on a common enemy
while remaining anonymous and avoiding retaliation. The strategy of nuclear
attack by proxy hinges on one key question: What is the likelihood that a coun-
try could sponsor a nuclear terror attack and remain anonymous? We examine
this question in two ways. 第一的, having no data on the aftermath of nuclear
terrorist incidents, we use the ample data on conventional terrorism to dis-
cover attribution rates. We examine the fraction of terrorist incidents attributed
to the perpetrating terrorist organization and the patterns in the rates of attri-
bution. 第二, we explore the challenge of tracing culpability for a nuclear
terror event from the guilty terrorist group back to its state sponsor. We ask:
How many suspects would there be in the wake of a nuclear detonation? 如何
many foreign terrorist organizations have state sponsors? Of those that do,
how many state sponsors do they typically have? And how many state spon-
sors of terrorism have nuclear weapons or sufªcient stockpiles of nuclear ma-
terials on which to base such a concern?
We conclude that neither a terror group nor a state sponsor would remain
anonymous after a nuclear terror attack. We draw this conclusion on the basis
of four main ªndings. 第一的, data on a decade of terrorist incidents reveal a
strong positive relationship between the number of fatalities caused in a terror
attack and the likelihood of attribution. Roughly three-quarters of the attacks
that kill 100 people or more are traced back to the perpetrators. 第二, attri-
bution rates are far higher for attacks on the U.S. homeland or the territory of a
major U.S. ally—97 percent (thirty-six of thirty-seven) for incidents that killed
ten or more people. 第三, tracing culpability from a guilty terrorist group
back to its state sponsor is not likely to be difªcult: few countries sponsor ter-
rorism; few terrorist groups have state sponsors; each sponsored terror group
has few sponsors (typically one); and only one country that sponsors terror-
主义, 巴基斯坦, has nuclear weapons or enough ªssile material to manufacture a
ternational Organization, 卷. 67, 不. 1 (冬天 2013), PP. 173–195; and Kyle Beardsley and Victor
Asal, “Nuclear Weapons as Shields,” Conºict Management and Peace Science, 卷. 26, 不. 3 (七月
2009), PP. 235–255. For earlier analyses, see Barry R. 波森, “我们. Security Policy in a Nuclear-
Armed World (或者: What If Iraq Had Had Nuclear Weapons?),” 安全研究, 卷. 6, 不. 3
(春天 1997), PP. 1–31; Jervis, The Meaning of the Nuclear Revolution, 小伙子. 1; and Richard K.
Betts, Nuclear Blackmail and Nuclear Balance (华盛顿, 华盛顿特区: 布鲁金斯学会出版社, 1987),
小伙子. 1–3, 6.
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国际安全 38:1 84
weapon. 总共, attribution of nuclear terror incidents would be easier than is
typically suggested, and passing weapons to terrorists would not offer coun-
tries an escape from the constraints of deterrence.12
This analysis has two important
implications for U.S. foreign policy.
第一的, the fear of terrorist transfer seems greatly exaggerated and does not—in
itself—seem to justify costly measures to prevent proliferation. Nuclear prolif-
eration poses risks, so working to prevent it should remain a U.S. foreign pol-
icy goal, but the dangers of a state giving nuclear weapons to terrorists have
been overstated, and thus arguments for taking costly steps to prevent prolif-
eration on those grounds—as used to justify the invasion of Iraq and fuel the
debate over attacking Iran—rest on a shaky foundation. 第二, analysts and
policymakers should stop understating the ability of the United States to
attribute terrorist attacks to their sponsoring states. Such rhetoric not only is
untrue, but it also undermines deterrence. States sometimes exaggerate their
capabilities to deter an enemy’s attacks;13 but U.S. analysts and leaders, 经过
understating U.S. attribution capabilities, inadvertently increase the odds of
catastrophic terrorist attacks on the United States and its allies.
The remainder of this article is divided into ªve main sections. The ªrst
section examines the logic that might tempt foreign leaders to give nuclear
materials to terrorists. The second section uses data from thousands of terror-
ist incidents to determine historical rates of attribution and critical patterns
in these data. The third section explores the challenge of linking terrorist
groups with their state sponsors. The fourth section rebuts several counter-
论据, and the conclusion discusses the implications of this analysis for
我们. foreign policy.
12. The danger of nuclear attack by proxy has two requirements: (1) that states be willing to trans-
fer such weapons or materials; 和 (2) that terrorist groups seek to carry out such destructive
attacks. 在本文中, we puncture the ªrst proposition. Other analysts debate the second, articu-
lated in Brian Jenkins’s classic statement that “terrorists want a lot of people watching and a lot of
people listening and not a lot of people dead.” See Jenkins, “International Terrorism: A New Mode
of Conºict,” in David Carlton and Carlo Schaerf, 编辑。, International Terrorism and World Security
(伦敦: Croom Helm, 1975), p. 15; Bruce Hoffman, Inside Terrorism (纽约: Columbia, 2006);
Mueller, Atomic Obsession, PP. 199–216; and Byman, “Iran, 恐怖主义, and Weapons of Mass De-
struction,” PP. 173, 179.
13. Two examples of leaders intentionally overstating their military capabilities are Nikita
Khrushchev’s exaggerated claims about the Soviet nuclear arsenal in the 1950s and, 最近,
Kim Jong-un’s faux intercontinental ballistic missiles (ICBMs) on parade in Pyongyang in 2012. 在
the former, see John J. 米尔斯海默, Why Leaders Lie: The Truth about Lying in International Politics
(纽约: 牛津大学出版社, 2011), PP. 31–32. On the latter, see Markus Schiller and Rob-
ert H. Schmucker, “A Dog and Pony Show: North Korea’s New ICBM,” Arms Control Wonk,
blog, 四月 18, 2012, http://lewis.armscontrolwonk.com/ªles/2012/04/KN-08_Analysis_Schiller
_Schmucker.pdf ; Jeffrey Lewis, “DPRK ICBM Items,“ 四月 19, 2012, Arms Control Wonk, http://
lewis.armscontrolwonk.com/archive/5150/dprk-icbm-items; and Jeffrey Lewis, “Real Fake Mis-
siles?” Arms Control Wonk, blog, 可能 1, 2012, http://lewis.armscontrolwonk.com/archive/5198/
real-fake-missiles.
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Why States Won’t Give Nuclear Weapons to Terrorists 85
The Logic of Nuclear Transfer to Terrorists: Assessing the Challenges
If a state were undeterrable—that is, if its leaders did not fear retaliation—
it would presumably conduct a nuclear strike itself rather than subcontract the
job to a terrorist group, ensuring that the weapons were used against the de-
sired target at the desired time (not against a target ultimately chosen by ter-
罗斯特). The calculated, “back-door” approach of transferring weapons to
terrorists makes sense only if a state fears retaliation. The core of the nuclear-
attack-by-proxy argument is that a state otherwise deterred by the threat of re-
taliation might conduct an attack if it could do so surreptitiously by passing
nuclear weapons to terrorists. Giving nuclear capability to a terrorist group
with which the state enjoys close relations and substantial trust could allow
the state to conduct the attack while avoiding devastating punishment.
Some analysts are skeptical about such sponsored nuclear terrorism, arguing
that a state may not be willing to deplete its small nuclear arsenal or stock of
precious nuclear materials. 更重要, a state sponsor would fear that a
terrorist organization might use the weapons or materials in ways the state
never intended, provoking retaliation that would destroy the regime.14 Nu-
clear weapons are the most powerful weapons a state can acquire, and hand-
ing that power to an actor over which the state has less than complete control
would be an enormous, epochal decision—one unlikely to be taken by regimes
that are typically obsessed with power and their own survival.
Perhaps the most important reason to doubt the nuclear-attack-by-proxy
scenario is the likelihood that the ultimate source of the weapon might be dis-
covered.15 One means of identifying the state source of a nuclear terrorist at-
tack is through “nuclear forensics”—the use of a bomb’s isotopic ªngerprints
to trace the ªssile material device back to the reactors, enrichment facilities, 或者
uranium mines from which it was derived. 理论上, the material that remains
after an explosion can yield crucial information about its source: the ratio of
uranium isotopes varies according to where the raw uranium was mined and
how it was processed, and the composition of weapons-grade plutonium re-
veals clues about the particular reactor used to produce it and how long the
material spent in the reactor.16 The possibility that the covert plot could be dis-
14. 看, 例如, Bunn, Securing the Bomb 2010, p. 20.
15. For examples of these arguments, see Mueller, Atomic Obsession, PP. 163–164, and sources cited
therein; and Falkenrath, 纽曼, and Thayer, America’s Achilles Heel. Note that even analysts
deeply concerned about the problem of nuclear terrorism arising from other sources (例如, theft or
black-market purchase of nuclear materials) can be more sanguine about the possibility of deliber-
ate state transfer. See Bunn, Securing the Bomb 2010, p. 20; and Matthew Bunn, “A Mathematical
Model of the Risk of Nuclear Terrorism,” Annals of the American Academy of Political and Social Sci-
恩斯, 卷. 607, 不. 1 (九月 2006), PP. 103–120, at pp. 115–116.
16. Nuclear weapons use uranium or plutonium as ªssile material—that is, the material that is
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国际安全 38:1 86
covered before being carried out also acts as a deterrent. For these and other
原因, some analysts argue that nuclear terrorism is unlikely.
Other policy analysts are more pessimistic. Many ªnd the attribution prob-
lem particularly signiªcant, largely because of the technical and political chal-
lenges involved in trying to pinpoint the source of nuclear material after
a detonation. They argue that the United States has not developed a reliable
and credible attribution capability, and they highlight the difªculty of build-
ing and maintaining strong nuclear forensic capabilities. A 2010 report by
the National Research Council, Nuclear Forensics: A Capability at Risk, found the
我们. ability to identify the source of nuclear explosive debris to be “fragile,
under-resourced and, in some respects, deteriorating.”17 The technical chal-
lenge of post-explosion forensics has been described as “among the most dif-
ªcult problems in physics.”18 In practice, signiªcant challenges arise from the
many bomb designs that could be used, as well as from the challenge of
building a comprehensive “library” with samples from all the world’s ura-
nium mines, centrifuges, reactors, and related sites. These challenges make it
daunting to determine with a high degree of conªdence the origin of nuclear
material through physical forensics.19 As a result, some analysts conclude
that nuclear attribution currently provides little deterrent value for coun-
tries that might consider diverting nuclear weapons or materials to terrorists.20
split to release the energy associated with a nuclear detonation. The uranium used in nuclear
weapons is typically U-235, a rare isotope that is acquired by separating the desired isotope from
the vastly more plentiful U-238. This separation (IE。, “enrichment”) can be done using various
方法; 现在, feeding uranium hexaºuoride gas through cascades of spinning centrifuges is
the most common approach. Plutonium is an element that does not exist in meaningful quantities
in nature; it is created in nuclear reactors as a by-product of ªssion.
17. National Research Council, Nuclear Forensics: A Capability at Risk, as cited in William J. Broad,
“Nuclear Forensics Skill Is Declining in U.S., Report Says,“ 纽约时报, 七月 29, 2010.
18. Michael Miller, “Nuclear Attribution as Deterrence,” Nonproliferation Review, 卷. 14, 不. 1
(行进 2007), p. 41.
19. Charles D. Ferguson, Preventing Catastrophic Nuclear Terrorism (纽约: Council on Foreign
关系, 2006), p. 6; and Miller, “Nuclear Attribution as Deterrence,” p. 40. The political obstacles
to establishing an effective nuclear attribution capability may be as challenging as the technical
那些. As one analyst observes, “The main problem with relying on nuclear forensics to identify
those responsible for a nuclear explosion . . . is the need to secure the cooperation of the same
countries that could be targets of a nuclear attribution investigation.” Richard Weitz, “Nuclear Fo-
rensics: False Hopes and Practical Realities,” Political Science Quarterly, 卷. 126, 不. 1 (春天
2011), PP. 54–55. 特别是, the likelihood of securing widespread participation by countries in
an international database of nuclear materials—which would entail contributing nuclear samples
and divulging highly sensitive information—is remote, given that the ultimate purpose of the en-
terprise is to identify and punish them if they misbehave or allow material to be stolen. This fun-
damental problem is compounded by additional practical factors: states that have previously
shared nuclear materials with other states have an incentive not to release samples that would im-
plicate them in these proliferation activities; states could submit false information or misleading
samples to hide past activity or frame a rival state; and states that legitimately sell or lease nuclear
reactor fuel to other countries would fear wrongful accusation if that material were used in an at-
tack. 同上。, PP. 55–66.
20. Broad, “Nuclear Forensics Skill Is Declining in U.S., Report Says.” Although the National Re-
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Why States Won’t Give Nuclear Weapons to Terrorists 87
Other pessimistic analyses highlight an important conundrum limiting the
ability of nuclear forensics to deter attack: deterrence would be bolstered if
the United States made more of its nuclear forensic capabilities public, 但
greater transparency would give terrorists and their potential sponsors greater
knowledge of weaknesses.
总共, pessimism about post-explosion attribution abounds. If one cannot
pinpoint those states responsible for the materials used in a terrorist nuclear
攻击, the ability to deter those states by threatening nuclear retaliation is
greatly weakened. The future sounds dire—but are these threats overblown?
Empirical Evidence from Terrorist Attacks
There have been no nuclear terror attacks, so it is impossible to directly test the
proposition that terrorists could conduct such attacks and remain anonymous.
In the past few decades, 然而, there have been thousands of conventional
terrorist incidents. It is thus possible to explore rates of attribution after those
incidents and seek patterns in the data that might shed light on the prospects
for attributing nuclear terrorism.21
search Council report is generally sanguine about the potential contribution of nuclear forensics to
the attribution mission, the report highlights several major areas of concern about U.S. 能力,
stemming from issues of organizational complexity, lack of direction, and lack of consensus; 的-
clining funding; skilled personnel spread too thin and working in outdated facilities; and outdated
equipment and procedures. National Research Council, Nuclear Forensics: A Capability at Risk
(华盛顿, 华盛顿特区: 美国国家科学院出版社, 2010). On other technical and political obstacles to
effective U.S. nuclear forensic capabilities, see Weitz, “Nuclear Forensics,” PP. 53–75; Michael M.
可能, Reza Aberdin-Zadeh, Donald Barr, Albert Carnesale, Philip E. Coyle, Jay Davis, 威廉
Dorland, William Dunlop, Steve Fetter, Alexander Glaser, Ian D. Hutcheon, Francis Slakey, 和
Benn Tannenbaum, Nuclear Forensics: Role, State of the Art, and Program Needs (华盛顿, 华盛顿特区:
American Association for the Advancement of Science Center for Science Technology and Security
政策, 二月 2008); 美国国家科学院, Making the Nation Safer: The Role of Science
and Technology in Countering Terrorism (华盛顿, 华盛顿特区: 美国国家科学院出版社, 2002); 和
Debra Decker, “Comments Provided for the Subcommittee on Oversight of Government Manage-
蒙特, the Federal Workforce, and the District of Columbia of the U.S. Senate Committee on Home-
land Security and Government Affairs Regarding the Status of U.S. Response Following a Nuclear
or RDD Attack,“ 十一月 15, 2007. Michael Miller, 然而, argues that the ºaws in nuclear fo-
rensic capabilities are “such that nuclear attribution currently provides little deterrent value.”
磨坊主, “Nuclear Attribution as Deterrence,” PP. 33–60, at p. 33. For a balanced analysis of the link
between improved nuclear forensics capabilities and the problem of deterring nuclear terrorism,
see Caitlin Talmadge, “Deterring a Nuclear 9/11,” Washington Quarterly, 卷. 30, 不. 2 (春天
2007), PP. 21–34.
21. Important works on “conventional” terrorism include Bruce Hoffman, Inside Terrorism (新的
约克: 哥伦比亚大学出版社, 2006); Daniel Byman, Deadly Connections: States That Sponsor Ter-
rorism (纽约: 剑桥大学出版社, 2005); Robert A. Pape, Dying to Win: The Strategic
Logic of Suicide Terrorism (伊萨卡岛, 纽约: 康奈尔大学出版社, 2005); 迈克尔·E. 棕色的, Owen R.
Coté Jr., Sean M. Lynn-Jones, and Steven E. 磨坊主, 编辑。, Contending with Terrorism: Roots, Strategies,
and Responsibilities (剑桥, 大量的。: 与新闻界, 2010); Audrey Kurth Cronin, How Terrorism
Ends: Understanding the Decline and Demise of Terrorist Campaigns (普林斯顿大学, 新泽西州: Princeton Univer-
城市出版社, 2011); and John Mueller and Mark G. 斯图尔特, “The Terrorism Delusion: America’s
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国际安全 38:1 88
数字 1. Terrorist Incidents and Rate of Attribution by Number of Fatalities
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To explore the history of terrorist attribution, we use the Global Terrorism
Database (GTD), a widely referenced dataset compiled by the National
Consortium for the Study of Terrorism and Responses to Terrorism, 哪个
includes incidents dating back to 1970.22 The version employed here ends in
2008 and includes more than 87,000 terrorist events. We use a subset of the
GTD data that includes 18,328 terrorist incidents that occurred from 1998 到
2008.23 We rely on this portion of the data because GTD ªrst started recording
whether terror groups claimed responsibility for an attack in 1998, an impor-
tant consideration in assessing the data on attribution rates.24
数字 1 shows the number of terror incidents that occurred from 1998 到
2008, and the rate of attribution, organized by the number of fatalities. 这
Overwrought Response to September 11,” International Security, 卷. 37, 不. 1 (夏天 2012),
PP. 81–110.
22. 国家恐怖主义研究和应对恐怖主义联盟 (START), 全球的
Terrorism Database (GTD), 2011, http://www.start.umd.edu/gtd.
23. The GTD dataset includes 20,234 incidents from 1998 到 2008. For two reasons, 然而, 我们的
consolidation of the data left us with 18,328 data points. 第一的, a large number of the attacks in the
GTD dataset are reported more than once. The GTD is designed to capture detailed information on
the weapons and tactics of terrorist groups, so an attack in which, 例如, terrorists detonated
a bomb outside a building and then armed men stormed the facility would be recorded as two in-
cidents. 为了我们的目的, it would introduce bias if we “double-counted” complex attacks, 所以
we consolidated the data to generate a single data point from each single attack. 第二, 因为
a key variable we explore is how attribution varies with fatality level, we ignored the roughly
2.5 percent of incidents for which the number of fatalities is not reported in the dataset.
24. We replicated our analysis with the Worldwide Incidents Tracking System (WITS) 数据库,
another major source for data on terrorist acts, and all the major ªndings reported here are
conªrmed. We have replicated ªgures 1 和 2 in this article using WITS data; they are available
from the authors upon request.
Why States Won’t Give Nuclear Weapons to Terrorists 89
solid line, corresponding to the logarithmic scale along the right y-axis, 印迪-
cates the number of terrorist incidents for each level of fatalities.25 The col-
umns, corresponding to the left y-axis, reveal the rate of attribution per fatality.
The data in ªgure 1 yield two key ªndings. 第一的, 的 18,328 attacks con-
ducted from 1998 到 2008, GTD researchers identiªed the attacker 42 的百分比
时间. That estimate of the “attribution rate,” however, implies greater pre-
cision than is warranted, because the researchers who coded the data did not
have all the information then or currently available to intelligence and law en-
forcement agencies. 所以, some cases that the researchers coded as “un-
attributed” may, 实际上, have been attributed; and on the other hand, 一些
the perpetrators identiªed in the GTD data set may have been incorrectly ac-
cused. Despite the possibility of errors in both directions, the data suggest that
the perpetrators of terror attacks are identiªed slightly less than half the time.
The implication of a 40–45 percent attribution rate is subject to competing
解释. 一方面, states that seek to retaliate after terrorist
attacks may desire a much higher rate of attribution. 另一方面, 从
the perspective of a potential perpetrator, knowing that a covert nuclear terror
attack has only about a 60 percent chance of remaining anonymous should
be sobering.
The second principal ªnding reºected in ªgure 1 is that the rate of attribu-
tion is strongly tied to the number of fatalities caused by the attack. Most terror
attacks kill relatively few people. 实际上, most of the incidents in the sample
caused 0 到 4 deaths; 并且只有 40 percent of those were attributed by GTD
to the perpetrator. But as fatalities increase, so does the rate of attribution. 的
这 49 attacks that killed more than 100 人们, the guilty party was identiªed
73 percent of the time. Based on these data, a terror group contemplating a
mass casualty attack should not expect to remain anonymous.
While ªgure 1 reveals a link between the level of fatalities and the likelihood
of attribution, most of the underlying data are derived from events unlike the
kind of incident that drives U.S. fears about proliferation and terrorism:
an anonymous nuclear terror strike on the United States or a U.S. 盟友. 这
18,000-plus cases in the dataset are mostly failed attacks, in foreign lands,
against target countries with less-capable intelligence agencies than those of
the United States and many key U.S. 盟国.
To shed more light on the prospect of attributing nuclear terror strikes on the
25. We use a logarithmic scale to allow readers to see the number of attacks, and how they decline,
as a function of fatalities. Because the data are skewed toward the low-fatality side of the distribu-
的, a linear scale would obscure the number of incidents that killed thirty or more people and the
variation among the high-fatality categories.
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国际安全 38:1 90
数字 2. Attribution Rates by Number of Fatalities: “我们. and Allies” and All Others
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United States or a key U.S. 盟友, we focused on a narrower subset of the GTD
data composed of attacks against the United States or its principal allies.26 We
also restricted the analysis to attacks on those states’ home territory—thereby
excluding incidents such as roadside bombings against military convoys in
distant lands. By focusing on attacks on the home soil of these countries, 我们
created a sample of 2,089 cases that provides greater leverage for evaluating
whether the United States or a close ally could be struck anonymously.
数字 2 compares the attribution rates for attacks against the United States
和美国. allies to attacks on the rest of the world. Two major observations
emerge from the data. 第一的, across all fatality levels, the United States and its
allies substantially outperform the “average” country in attributing terrorist
incidents. 第二, the rate of attribution for the United States and its allies in-
creases as a function of fatalities—as do the aggregate data in ªgure 1, 但
more steeply and reaching higher levels. 特别是, the United States and its
allies suffered thirty-seven homeland attacks that killed ten or more people
and identiªed the perpetrators in thirty-six of those cases (97 百分). 一
should not infer from this that the United States and U.S. allies are the best at
26. For this group, we counted the United States; other NATO members; and Australia, 以色列, Ja-
pan, 和韩国. Some countries became members of NATO during the decade in question;
we counted attacks on their territory starting the year in which they joined the alliance.
Why States Won’t Give Nuclear Weapons to Terrorists 91
attributing attacks—some other countries (例如, 俄罗斯) also have high attribu-
tion rates. The claim is merely that when terrorists kill even a moderate num-
ber of Americans or citizens of U.S. allies on their home soil, the perpetrators
are almost always identiªed.
The data presented in ªgures 1 和 2 include cases in which terror groups
claim responsibility for their attacks and those in which they do not. Even the
cases in which the guilty terror group takes responsibility should be consid-
ered “successful attribution,” because successful attacks often induce multiple
groups to take credit—requiring the victim to evaluate the competing claims
and also look for possible culprits among those who have not taken credit.
此外, in some cases the attacks were attributed before the claims of re-
sponsibility were issued (例如, 九月 11 attacks were attrib-
uted to al-Qaida before the group claimed responsibility). For both of those
原因, removing the “claimed” cases from the dataset may exclude many
cases of successful attribution.
尽管如此, ªgure 3 displays data on the subset of cases in which the
guilty party never claimed credit for the attack. As the ªgure reveals, 联合国-
claimed cases look similar to the claimed ones: the likelihood of attribution in-
creases with the number of fatalities, especially for attacks on the “U.S. 和
allies.” Furthermore, even when incidents produced only moderate fatalities
(5-plus people killed), the United States and its allies identiªed the perpetra-
托尔斯 83 percent of the time—a rate that should chasten those who might pass
nuclear weapons to terrorists.
合在一起, the data on conventional terrorism suggest that nuclear
attacks—especially those that target countries with sophisticated intelligence
agencies—would not remain anonymous for long. 实际上, both because of its
shocking nature and because of fears of an additional follow-up nuclear terror
攻击, any instance of nuclear terror would trigger an unprecedented global
调查. The data in this section, 所以, likely understate the probabil-
ity of attribution. For a state leader contemplating giving a nuclear weapon to
terrorists, the implication is clear: your proxy will very likely be identiªed.
Linking Terrorists to Their Sponsors
The data presented above reveal that devastating attacks are usually attributed
to the responsible terrorist organization. But to deter states from passing nu-
clear weapons or materials to terrorists, one must also be able to connect the
terrorists to their state sponsor. How difªcult would it be to do this?
Passing nuclear weapons or material to a terrorist group under any circum-
stances would be a remarkably risky act. A leader who sponsored nuclear ter-
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国际安全 38:1 92
数字 3. Attribution after Unclaimed Attacks
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rorism would be wagering his life, the lives of family members, his regime,
and his country’s fate on the hope that the operation would remain anony-
mous. If the terror group used the weapon against a different enemy or re-
vealed the source of the weapon, or if the terror group’s operatives or senior
leadership were penetrated by foreign intelligence, the consequences could be
catastrophic for the sponsor.
Given the enormous risks involved, it is difªcult to imagine a state’s leaders
placing so much faith in a terrorist organization unless they already had a
long-running, close, and trusting relationship with that group, and unless that
group had repeatedly demonstrated its reliability, competence, and ability to
maintain secrecy. 此外, leaders considering giving nuclear weapons
to terror groups would need to ªnd a group with the demonstrated capabil-
ity to conduct complex operations across international borders.27 Many violent
nonstate groups can plant roadside bombs or conduct small-scale ambushes
against unsuspecting targets, but those relatively simple attacks do not imply
an ability to conduct complex international operations involving training,
27. For a thorough discussion of the task, see Mueller, Atomic Obsession, PP. 161–198.
Why States Won’t Give Nuclear Weapons to Terrorists 93
travel, visas, ªnances, and secure communications.28 In short, both the com-
plexities of the mission and the need for unwavering trust mean that a state
seeking to orchestrate a nuclear attack by proxy would be limited to collabora-
tions with well-established terrorist organizations with which it has existing
关系, simplifying the task of connecting terrorist perpetrators to their
state sponsors.
To assess the difªculty of connecting terrorists to their sponsors, we com-
piled a list of terror organizations—focusing on those with close relationships
to one or more countries. We began with the U.S. State Department’s list of for-
eign terrorist organizations (FTOs), which we then adjusted, as described be-
低的, to account for potential omissions.29 The adjustments generally involved
adding state-sponsored terror groups to the State Department’s list, 哪个, 经过
本身, would make it harder to establish our claim that victims could trace at-
tacks from guilty terrorists to their sponsors.
According to the State Department, there are ªfty-one FTOs, only nine of
which have state sponsors.30 Furthermore, according to the State Department,
only four countries actively sponsor terror groups: Cuba,
伊朗, 利比亚,
and Syria.31
28. 例如, a complex international terror operation, such as the September 11 terrorist
attacks, requires loyal and competent operatives who can travel to the target state. This often
involves gaining entrance visas, establishing secure communication procedures, training the oper-
atives to conduct the mission, moving money across borders, and moving the weapon itself to the
victim state. As the September 11 attacks illustrate, sophisticated terrorist groups such as al-Qaida
can execute complex operations such as these, but the organizational requirements are far more
advanced than the capabilities of local militias and most terrorist groups.
29. 我们. Department of State, “Foreign Terrorist Organizations,“ 九月 28, 2012, http://
www.state.gov/j/ct/rls/other/des/123085.htm. For a description of each foreign terrorist organi-
扎化 (FTO), see U.S. Department of State, “Country Report on Terrorism, 2011” (华盛顿,
华盛顿特区: 我们. Department of State, 七月 31, 2012), 小伙子. 6, http://www.state.gov/j/ct/rls/crt/. 这
State Department deªnes an FTO as a group that either engages in terrorism or retains the capabil-
ity and intent to do so and whose terrorist activities threaten the citizens or interests of the United
状态. The last criterion means that the list principally includes anti-American terrorists, 但它是
nevertheless useful for two reasons. 第一的, even though the list excludes terror groups whose inter-
ests align with those of the United States, unless “anti-American” terrorist groups have, 平均-
年龄, signiªcantly fewer or signiªcantly more state sponsors than pro-American terror groups, 这
State Department list offers good insight into the number of state sponsors per terrorist group.
第二, although one purpose of this article is to explore the challenge of terrorist attribution gen-
埃拉利, a related goal is to explore the challenge of attribution for the United States. The terrorist or-
ganizations excluded from this list would not be prime suspects in a nuclear terror strike against
美国.
30. The number of FTOs comes from U.S. Department of State, “Foreign Terrorist Organizations.”
The number of FTOs with state sponsors is culled from U.S. Department of State, “Country Report
on Terrorism, 2011.”
31. The State Department also lists Sudan on its list of state sponsors of terror, but only because of
Sudan’s inability to adequately police its territory (and hence to effectively combat terrorist groups
on its own territory). The State Department does not claim that Sudan funds, 武器, or gives safe
haven to any FTO.
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国际安全 38:1 94
桌子 1. State-Sponsored Foreign Terrorist Organizations (FTOs)
叙利亚
✔
✔
✔
✔
✔
✔
Popular Front for the
Liberation of Palestine
Abu Nidal Organization
Hamas
Hezbollah
Palestinian Islamic Jihad
Popular Front for the
Liberation of Palestine—
General Command
Al-Aqsa Martyrs Brigade
Kata’ib Hezbollah
Al-Qaida
Haqqani Network
Indian Mujahideen
Jaish-e-Mohammed
Lashkar-e-Tayiba
National Liberation Army
Revolutionary Armed
Forces of Colombia
伊朗
利比亚
巴基斯坦
委内瑞拉
Cuba
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
笔记: Shading indicates the only FTOs that have multiple sponsors. Pakistan is the only spon-
sor of terrorism that has bomb quantities of ªssile material. No FTO has multiple nuclear-
capable sponsors, which would remain true even if Iran acquires nuclear weapons.
We made three signiªcant adjustments to this list. Some experts argue that
the State Department understates Pakistan’s and Venezuela’s roles in support-
ing various FTOs, so we added four FTOs that are alleged to have close ties to
Pakistan and two that are often linked to Venezuela.32 Furthermore, several
terror experts note that al-Qaida has meaningful ties with Iran, even if their
relationship is plagued by substantial distrust.33 (例如, Iran has held
32. 在 2008, Pakistan was described as “perhaps the world’s most active sponsor of terrorist
groups.” Daniel L. Byman, “The Changing Nature of State Sponsorship of Terrorism,” Saban Cen-
ter Analysis Paper Series (华盛顿, 华盛顿特区: 布鲁金斯学会, 可能 2008), p. 7. On Pakistan’s
more recent support for terrorists, see Peter Tomsen, “Pakistan: With Friends Like These . . .” World
Policy Journal, 卷. 28, 不. 3 (九月 2011), PP. 82–90. The Pakistan-linked groups are Lashkar-
e-Taiba, Jaish-e-Mohammed, the Haqqani Network, and the Indian Mujahedeen. The groups
linked to Venezuela are the Revolutionary Armed Forces of Colombia and the National Liberation
Army. See Mark P. Sullivan, “Venezuela: Issues for Congress” (华盛顿, 华盛顿特区: Congressional
Research Service, 十月 12, 2012).
33. Daniel L. Byman, “Unlikely Alliance: Iran’s Secretive Relationship with Al-Qaeda,” Iranian
Sponsorship of Terrorism, IHS Defense, 风险, and Security Consulting, 七月 2012.
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Why States Won’t Give Nuclear Weapons to Terrorists 95
key al-Qaida members and their families hostage, perhaps in order to deter
al-Qaida from attacking Iran or to gain release of Iranian hostages held by the
organization.34 But because ties between the state and the group exist, 我们在-
clude al-Qaida on our list.) We are thus left with ªfteen terror groups and six
states that sponsor terrorism (见表 1).35
桌子 1 appears to present a daunting list of FTOs and states, but the data
show that tracing an attack from a terror group to its sponsor would be rela-
tively simple. 第一的, nearly all of the terror groups listed have only one or two
sponsors: nine FTOs have a single sponsor; ªve have two sponsors; 并且只有
one—the Abu Nidal Organization—has three (and it might soon have only a
single sponsor).36 此外, only one of the sponsors has nuclear weapons
or bomb quantities of ªssile material (巴基斯坦). If Pakistan were to consider
giving a weapon to terrorists, it would not turn to Hezbollah or Hamas, 和
which it has weak connections. 也不, for the same reason, would Iran give nu-
clear weapons or material to Jaish-e-Mohammed. The implication is clear: if a
terrorist group is identiªed in a nuclear attack, the list of possible sponsors will
be short. In almost every conceivable case, a single nuclear-armed suspect
will stand out.
最后, 桌子 1 does not capture the momentous changes under way in the
中东. It is unclear whether post-Qaddaª Libya will continue to sponsor
terrorism or whether Syria (currently enmeshed in civil war) will remain a
sponsor for long. If those two states were to cease supporting FTOs, then no
FTO would have more than a single sponsor—making it simple to trace an at-
tack from an identiªed group to the country that supplied it.
This discussion highlights the fundamental conundrum for a country seek-
ing to sponsor nuclear terror: given the incredible risks, it must collaborate
with a group that it trusts completely. 同时, it must choose a terror
partner with whom it has weak (and hence untraceable) 领带. These two goals
are fundamentally contradictory. Only a terrorist group with a long association
and deep ties (and a record of effective operations) could be trusted with a
核武器; such a group, 然而, would be unlikely to stay below the
radar of Western intelligence agencies and hide those close ties.
34. Mark Hosenball, “Documents Show Tense Al Qaeda Relationship,” 路透社, 可能 3, 2012.
35. Other critics question North Korea’s absence from the State Department’s list of FTOs. 上
decision to remove North Korea from the list, see Helene Cooper, “我们. Declares North Korea off
Terror List,“ 纽约时报, 十月 12, 2008. Although the North Korean government has carried
out numerous attacks against South Korea over the past ªve decades, the North Korean military
conducted those attacks, not terrorist groups. For a discussion of these attacks, see Jennifer Lind,
“Why North Korea Gets Away With It,” Snapshot, 外交事务, 四月 12, 2012, http://万维网
.foreignaffairs.com/articles/137399/jennifer-lind/why-north-korea-gets-away-with-it.
36. Given regime change in Libya and the civil war in Syria, it is unclear whether the organization
will continue to receive signiªcant support from those states.
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国际安全 38:1 96
Counterarguments
Critics of our analysis might offer several counterarguments. 第一的, 问题-
lem of “loose nukes” might give state sponsors of nuclear terrorism an oppor-
tunity for avoiding responsibility for their actions. 第二, one might discount
empirical evidence about the attribution rate of conventional terror attacks be-
cause attributing a nuclear attack would be different—and harder—than at-
tributing an act of conventional terrorism. 第三, one might argue that some
states will still be tempted to resort to nuclear attack by proxy because the
threat of retaliation by the victim would lack credibility given the inherent un-
certainty that would persist even in a case of so-called successful attribution.
counterargument #1: capitalizing on “loose nukes”
In the wake of a nuclear detonation, investigators would need to consider the
possibility that the nuclear device or ªssile materials were obtained without
the consent of any state. The attack might not have resulted from a state’s
attack-by-proxy strategy, but rather from the problem of “loose nukes”—
poorly secured nuclear weapons or materials falling into the wrong hands
through illicit means. Knowing that a victim would need to at least consider
the possibility of nuclear theft, a state sponsor might hope to succeed with its
nuclear handoff under one of two logics. 第一的, a state might give nuclear
weapons or materials to a terrorist organization with full awareness that it
would be identiªed as the source, but then try to avoid responsibility by claim-
ing that the weapons or materials had been stolen from its stockpiles. 第二,
a state might give nuclear weapons or materials to a terrorist organization and
try to avoid responsibility by claiming that the weapons or materials were sto-
len from a different foreign stockpile.
The ªrst strategy—giving nuclear weapons to terrorists and then pleading
guilty to the lesser charge of maintaining inadequate stockpile security—is
highly dubious. Any state rational enough to seek to avoid retaliation for a nu-
clear attack would recognize the incredible risk that this strategy entails. 在
the wake of an act of nuclear terrorism, facing an enraged and vindictive vic-
蒂姆, would the state sponsor step forward to admit that its weapons or materi-
als were used to attack a staunch enemy, with the hope that the victim would
believe a story about theft and grant clemency on those grounds? If that logic
does not appear implausible enough, recall that no state would be likely to
give its nuclear weapons or materials to a terrorist organization with which it
did not have a long record of cooperation and trust. 因此, a state sponsor ac-
knowledging that it was the source of materials used in a nuclear attack would
be doing so in light of its enemies’ knowledge that the terrorists who allegedly
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Why States Won’t Give Nuclear Weapons to Terrorists 97
stole the materials happened to have been its close collaborators in prior acts
of terrorism. This strategy would be nearly as suicidal as launching a direct
nuclear attack.37
The second strategy—giving nuclear weapons to terrorists and then hiding
behind the possibility that they were stolen from some unspeciªed insecure
foreign source—deserves greater scrutiny. The list of potential global sources
of ªssile material seems long. Nine countries possess nuclear weapons, 和
eleven more have enough ªssile material to fashion a crude ªssion device.38 In
2011 the world’s stockpile of highly enriched uranium (HEU), the ªssile mate-
rial most likely to be sought by terrorists,39 was about 1.3 million kilograms,
meaning that the material needed for a single crude weapon could be found
within the rounding error of the rounding error of global stocks. 也许,
所以, nearly all twenty countries with sufªcient stocks of ªssile material
would need to join the lineup of suspects after a terrorist nuclear attack, not as
possible sponsors but as potential victims of theft. And if enough ªssile mate-
rial to make a nuclear weapon could be purloined from any of these countries,
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37. 例如, if Israel suffered a nuclear attack, and Tehran admitted that the weapon used
was Iranian but blamed Hezbollah for stealing it, it is unlikely that Israel would believe Iran’s
故事. It might not temper its response even if it did, because it could be argued that Iran’s long
history of support for Hezbollah makes Tehran responsible for Hezbollah’s actions.
38. The nine states with nuclear weapons are China, 法国, 印度, 以色列, 北朝鲜, 巴基斯坦,
俄罗斯, 英国, 和美国. The eleven states with at least 15 kilograms of
highly enriched uranium or about 5 kilograms of plutonium—the minimum threshold considered
necessary to build a crude nuclear device—are Belarus, 比利时, 加拿大, the Czech Republic,
德国, 意大利, 日本, Kazakhstan, 荷兰人, 波兰, and South Africa. On ªssile material
thresholds, see International Panel on Fissile Materials, Global Fissile Material Report 2011 (王子-
吨, 新泽西州: Program on Science and Global Security, 普林斯顿大学, 2011), p. 27. On the coun-
tries meeting these minimum thresholds, see ibid.; James Martin Center for Nonproliferation
学习, “Civil Highly Enriched Uranium: Who Has What?” http://www.nti.org/media/pdfs/
HEU_who_has _what.pdf; and Ofªce of the Press Secretary, “Fact Sheet: Ukraine Highly Enriched
Uranium Removal,” Washington, 华盛顿特区, 行进 27, 2012, http://www.whitehouse.gov/the-press-
ofªce/2012/03/27/fact-sheet-ukraine-highly-enriched-uranium-removal. Although we credit any
state with 15 kilograms of HEU as having bomb quantities of ªssile material, a uranium-based
weapon constructed by terrorists would likely be a simple design (perhaps a “gun-type” weapon)
that would require substantially more than 15 kilograms of HEU—possibly in the 50-kilogram
范围. 看, 例如, 忧思科学家联盟 (UCS), “Weapon Materials Basics” (凸轮-
桥, 大量的。: UCS, 四月 2004), http://www.ucsusa.org/nuclear_weapons_and_global_security/
nuclear_terrorism/technical_issues/ªssile-materials-basics.html; and “Nuclear Terrorism 101”
(剑桥, 大量的。: Belfer Center for Science and International Affairs, Harvard Kennedy School,
日期不详。), http://nuclearsummit .org/nuclear_terrorism_101.html.
39. HEU is less radioactive than plutonium and is therefore easier to handle and harder for sen-
sors to detect. HEU can also be used in a crude gun-type ªssion bomb, a relatively simple device
to build. Plutonium, 相比之下, is highly radioactive and therefore difªcult to handle without in-
ducing debilitating radiation poisoning; it is easier to detect; and it must be detonated through a
sophisticated implosion device, which is technically demanding to build—probably beyond the
capabilities of terrorist groups.
国际安全 38:1 98
then perhaps the victim would be unable to rule out all possible sources
and thus be unable to punish the real culprit.
This gloomy picture overstates the difªculty of determining the source of
stolen material after a nuclear terrorist attack. In the wake of a detonation, 这
possibility of stolen ªssile material complicates the task of attribution—but
only marginally. At the end of the Cold War, several countries—particularly in
the former Soviet Union—confronted major nuclear security problems, 但
great progress has been made since then.40 Although no country has perfect
nuclear security, today the greatest concerns surround just ªve countries:
Belarus, 日本, 巴基斯坦, 俄罗斯, and South Africa.41 In addition, not all of
those states are equally worrisome as potential sources of nuclear theft. Sub-
stantial concerns exist about the security of ªssile materials in Pakistan and
俄罗斯 (the latter if simply because of the large size of its stockpile), 但
Belarus, 日本, and South Africa would likely be quickly and easily ruled out
as the source of stolen ªssile material. Belarus has a relatively small stockpile
of ªssile material—approximately 100 kilograms of HEU42—so in the wake of
a nuclear terrorist attack, it would be easy for Belarus to show that its stockpile
remained intact.43 Similarly, 日本 (one of the United States’ closest allies) 和
40. Bunn, Securing the Bomb 2010, p. 23–59, gives a detailed account of the progress in securing nu-
clear material and the remaining risks. Note that our focus in this article is on the security of ªssile
材料, not weapons. All nine nuclear weapon states place great emphasis on security at their
nuclear weapons storage sites. Even Pakistan, the country that rightfully inspires the greatest nu-
clear security concerns, keeps its weapons consolidated at a small number of highly defended fa-
城市, and apparently stores its weapons disassembled with each nuclear core located separately
from the rest of the device. On Pakistan storing its weapons disassembled, see Hans M. Kristensen
and Robert S. Norris, “Pakistan’s Nuclear Forces, 2011,” Bulletin of the Atomic Scientists, 卷. 67,
不. 4 (七月八月 2011), PP. 91–99; and David Albright, “Securing Pakistan’s Nuclear Infrastruc-
真实,” in Lee Feinstein, James Clad, Lewis Dunn, and David Albright, A New Equation: 我们. 政策
toward India and Pakistan after September 11 (华盛顿, 华盛顿特区: Carnegie Endowment for Interna-
tional Peace, 2002). 此外, most nuclear weapons have sophisticated, integrated locks to
prevent unauthorized detonation.
41. According to the Fissile Materials Working Group, “The stocks of nuclear weapons or weap-
ons-usable nuclear material that are most likely to fall into terrorist hands today exist in Russia,
巴基斯坦, and countries with research reactors that use large quantities of highly enriched uranium
(HEU)—like Belarus, 南非, and Japan.” Fissile Materials Working Group, “Nuclear Secu-
rity’s Top Priority,” Bulletin of the Atomic Scientists, online edition, 六月 12, 2012, http://万维网
.thebulletin.org/web-edition/columnists/ªssile-materials-working-group/nuclear-securitys-top-
priority. See also Bunn, Securing the Bomb 2010, PP. 27–43, on risks emanating from Russia and Pa-
kistan, and pp. 43–45 on risks at HEU research reactors. Bunn identiªes Belarus, Kazakhstan, 和
South Africa as posing the greatest dangers, as summarized in Bunn, Securing the Bomb 2010, 桌子
3.5. Bunn’s list of top concerns includes Kazakhstan, but that country has subsequently eliminated
almost all of its highly enriched uranium, and its remaining stock—mostly in the range of 22 到
36 percent enrichment—would be inordinately difªcult for a terror group to process into material
for a nuclear bomb. Bunn’s discussion also includes Ukraine, but Ukraine has subsequently re-
moved all HEU from its territory. On Ukraine, see Ofªce of the Press Secretary, “Fact Sheet:
Ukraine Highly Enriched Uranium Removal.”
42. Fissile Materials Working Group, “Nuclear Security’s Top Priority.”
43. As discussed above, a crude, gun-type HEU bomb—the type that terrorists might be able to
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Why States Won’t Give Nuclear Weapons to Terrorists 99
South Africa would be keen to allow the United States to verify the integrity of
their full stocks of materials. (In the wake of a nuclear terror attack, a lack
of full cooperation in showing all materials accounted for would be highly re-
vealing.) Iran is not believed to have any weapons-usable nuclear material to
steal,44 although that could change. 简而言之, a nuclear handoff strategy dis-
guised as a loose nukes problem would be very precarious.45
counterargument #2: conventional versus nuclear attribution
The evidence presented above shows that the perpetrators of terror attacks
against the United States or its allies in which ten or more people are killed on
home territory are almost always identiªed. But these data are based solely on
conventional terror attacks. Might acts of nuclear terror be harder to attribute
than their conventional cousins?
With no actual cases of nuclear terrorism to examine, it is impossible to
know for sure how the challenges of attribution after a nuclear attack would
compare to the difªcult police and intelligence work that led to attribution in
the thousands of cases of conventional terrorism. Logic suggests at least one
reason why it might be harder to identify the perpetrators of nuclear terrorism,
but many other factors suggest that nuclear attribution would be easier than
solving conventional incidents of terrorism. 合在一起, these arguments
suggest that the data presented above may well understate the actual likeli-
hood of nuclear attribution.
Identifying the perpetrators of a nuclear terror attack, as opposed to a con-
ventional terror incident, would be harder because a nuclear detonation would
destroy much of the evidence near the site of the attack. In the aftermath of a
conventional bombing, investigators check nearby security cameras for images
of the attackers, sift through the debris to recover physical evidence, and inter-
view witnesses. This sort of evidence has proved useful in several terror inves-
tigations. 例如, investigators found the vehicle identiªcation number
(VIN) from the trucks used to bomb the World Trade Center in 1993 and to de-
stroy the Alfred P. Murrah Federal Building in Oklahoma City in 1995.46 A nu-
clear detonation, 然而, would leave little (如果有的话) of such evidence.
construct—requires roughly 50 kilograms of HEU, approximately half of Belarus’s entire stockpile.
It would be simple for Belarus to demonstrate its innocence.
44. Bunn, Securing the Bomb 2010, p. 21. Iran has roughly 7 kilograms of irradiated research reactor
燃料.
45. Similar to the ªrst strategy, this strategy of trying to capitalize on the problem of loose nukes
is confounded by the need for the state sponsor to work with terrorist groups with which they
have had long-established relations. 例如, if a terrorist nuclear attack were attributed to
Lashkar-e-Taiba, it would seem impossible for Pakistan to pin the blame for stolen ªssile materials
on Japan or South Africa.
46. 罗伯特·L. Jackson, “Bomb Case Built a Stub, a Shard, a Shell at a Time,” 洛杉矶时报, 的-
十二月 13, 1993; “Turning to Evidence; Axle and Fingerprints,” Kingman Daily Miner, 四月 29,
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国际安全 38:1 100
Although investigators always prefer to have physical evidence from the
scene of a bombing, in high-proªle investigations such evidence is used in con-
junction with vast quantities of other data: 例如, information about the
activities of terror groups already under surveillance before the attack; 国际米兰-
cepted cellphone and internet communications; reports from agents embed-
ded with known terror groups; and similar types of information shared by
friendly governments. 实际上, while the VIN number was useful in solving
这 1993 World Trade Center attack, it was far less important in the Oklahoma
City bombing investigation, because the key suspect was in custody before the
on-site evidence was gathered. 尽管如此, the loss of evidence from the at-
tack site would complicate the attribution of a nuclear terror attack relative to
a conventional terror incident.
There are at least ªve reasons, 然而, to expect that attributing a nuclear
terrorist attack would be easier than attributing a conventional terrorist attack.
第一的, no terrorism investigation in history has had the resources that would be
deployed to investigating the source of a nuclear terror attack—particularly
one against the United States or a U.S. 盟友. Rapidly attributing the attack
would be critical, not merely as a ªrst step toward satisfying the rage of the
victims but, more importantly, to determine whether additional nuclear at-
tacks were imminent. The victim would use every resource at its disposal—
钱, 威胁, and force—to rapidly identify the source of the attack.47 If
必要的, any investigation would go on for a long time; it would never “blow
over” from the victim’s standpoint.
The second reason why attributing a nuclear terror attack would be
easier than attributing a conventional terrorist attack is the level of interna-
tional assistance the victim would likely receive from allies, neutrals, 乃至
adversaries. An attack on the United States, 例如, would likely trigger
unprecedented intelligence cooperation from its allies, if for no other reason
than the fear that subsequent attacks might target them. Perhaps more impor-
坦特, even adversaries of the United States—particularly those with access to
ªssile materials—would have enormous incentives to quickly demonstrate
their innocence. To avoid being accused of sponsoring or supporting the at-
tack, and thus to avoid the wrath of the United States, these countries would
likely go to great lengths to demonstrate that their weapons were accounted
为了, that their ªssile materials had different isotopic properties than the type
used in the attack, and that they were sharing any information they had on the
1997; 和理查德·A. Serrano, “McVeigh Guilty in Bombing: Death Penalty Trial Next in Okla-
homa Tragedy,” 洛杉矶时报, 六月 3, 1997, text of infobox.
47. It is possible that the strong positive relationship between attribution rate and fatalities,
as shown in ªgures 1 到 3, is a reºection of the greater investigative resources devoted to higher-
fatality terror attacks.
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Why States Won’t Give Nuclear Weapons to Terrorists 101
攻击. The cooperation that the United States received from Iran and Pakistan
in the wake of the September 11 attacks illustrates how potential adversaries
may be motivated to help in the aftermath of an attack and stay off the target
list for retaliation.48 The pressure to cooperate after an anonymous nuclear det-
onation on U.S. soil would be many times greater.49
第三, the strong positive relationship between the number of fatalities
stemming from an attack and the rate of attribution (as depicted in ªgures 1
到 3 多于) suggests that the probability of attribution after a nuclear attack—
with its enormous casualties—should be even higher. 这 97 percent attribu-
tion rate for attacks that killed ten or more people on U.S. soil or that of its
allies is based on a set of attacks that were pinpricks compared to nuclear ter-
rorism. The data in those ªgures suggest that our conclusions understate the
actual likelihood of nuclear attribution.
第四, the challenge of attribution after a terrorist nuclear attack should
be easier than after a conventional terrorist attack, because the investigation
would begin with a highly restricted suspect list. In the case of a conventional
terror attack against the United States or an ally, one might begin the investiga-
tion at the broadest level with the U.S. Department of State’s list of ªfty-one
foreign terrorist organizations. In the case of a nuclear terror attack, 仅有的
ªfteen of these FTOs have state sponsors—and only one sponsor (巴基斯坦)
has either nuclear weapons or ªssile materials. (If Iran acquires nuclear weap-
昂斯, that number will grow to two, but there is no overlap between the terror
groups that Pakistan supports and those that Iran assists.)
最后, any operation to detonate a nuclear weapon would involve complex
planning and coordination—securing the weapon, learning to use it, 规划
the time and location of detonation, moving the weapon to the target, 和骗局-
ducting the attack. Even if only a small cadre of operatives knew the nuclear na-
ture of the attack, the planning of a spectacular operation would be hard to keep
48. James Dobbins, “Engaging Iran,” in Robin B. 赖特, 编辑。, The Iran Primer: 力量, 政治, 和
我们. 政策 (华盛顿, 华盛顿特区: United States Institute of Peace Press, 2010), 小伙子. 47. After the Sep-
木材 11 attacks, Pakistan captured terrorist suspects, allowed the United States to use Pakistani
airports and bases for operations into Afghanistan, and provided other kinds of logistical support.
49. The United States invasion of Iraq in 2003 arguably created another incentive for states to co-
operate in any investigation. The United States attacked Iraq, toppled its regime, and spent bil-
lions of dollars waging a war that devastated the country—even though the evidence connecting
Saddam Hussein to September 11, al-Qaida, or the active pursuit of weapons of mass destruction
was extraordinarily ºimsy. Those actions, despite many other costs to the United States and its in-
兴趣, likely bought the United States a heavy measure of future cooperation from countries seek-
ing to prove their innocence in the wake of a nuclear terrorist attack. One might argue that some
states would withhold cooperation with a future U.S. investigation so as not to be responsible for
assisting in the initiation of a massive retaliatory war launched by the United States against the
state sponsor. States are unlikely, 然而, to value these reputational consequences above their
own security interests, which would be jeopardized by noncooperation with the United States af-
ter a nuclear terror attack.
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国际安全 38:1 102
secret.50 For example, six months prior to the September 11 attacks, Western in-
telligence detected numerous indications that al-Qaida was planning a major at-
tack. The intelligence was not speciªc enough—or the agencies were not nimble
enough—to prevent the operation, but the indicators were “blinking red” for
月, directing U.S. attention to al-Qaida as soon as the attacks began.51
counterargument #3: uncertainty and failed deterrence
Skeptics of our conªdence in the feasibility of post-nuclear attack attribution
might emphasize the role of uncertainty in constraining the response of the
victim. 归因, 毕竟, is not a binary outcome but a matter of probabili-
领带. Each of the cases of “successful attribution” in the data we used reºects
a consensus among GTD researchers that a particular group carried out an
attack—but there are few cases in which the list of the guilty parties is certain.
Without such certainty, a victim of nuclear terrorism would arguably be con-
strained in its response against a suspected sponsor. Believing this, a state
comparing the option of a direct nuclear attack to sponsorship of a terrorist
strike might prefer the latter, counting on residual attribution uncertainty to
dampen the response.
There are two problems with this counterargument. 第一的, while attribution
uncertainty might restrain a state from responding to an act of nuclear terror
with a major nuclear retaliatory strike, that option is not the only devastating re-
sponse available to a country such as the United States or one of its allies. 在-
契据, regardless of the level of attribution certainty, a nuclear strike might not be
the preferred response. 例如, in the wake of a nuclear terror attack
against the United States thought to be sponsored by Pakistan, 伊朗, or North
韩国, 我们. leaders might not feel compelled to determine those countries’ guilt
“beyond a reasonable doubt” or to narrow down the suspect list further; Wash-
ington might simply decide that the era in which “rogue states” possessed nu-
clear weapons must end, and threaten to conquer any country that refused to
disarm or that was less than forthcoming about the terror attack.52
第二, this counterargument would be unlikely to carry much weight with
a leader contemplating nuclear attack by proxy. A leader tempted to attack be-
cause of the prospect of residual attribution uncertainty and the hope that such
uncertainty would restrain his victim from lashing out in retaliation would
need enormous conªdence in the humaneness of his enemy, even at a time
50. Mueller, Atomic Obsession, 小伙子. 12, 13.
51. “这 9/11 Commission Report,” chap. 8.
52. There is precedent for this approach. When Japan attacked Pearl Harbor, 美国
framed the attack in a broader context—not solely about the evils of Japan, but the need to stop the
Axis—setting the United States down a course to conquer Germany, 意大利, and Japan—three far
more powerful states in relative conventional terms than Iran, 北朝鲜, and Pakistan today.
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Why States Won’t Give Nuclear Weapons to Terrorists 103
when that enemy would be boiling over with rage. 例如, could one re-
ally imagine an Iranian aide convincing the supreme leader that if Iran gave a
nuclear bomb to Hezbollah, knowing that Israel would strongly suspect Iran
as the source, Israel’s leaders would be too restrained by their deep humanity
and lingering doubts about sponsorship to retaliate harshly against Tehran?
实际上, 美国. response to the September 11 attacks, including the inva-
sions of Afghanistan and Iraq, indicates a willingness to retaliate strongly
against those directly culpable (al-Qaida), their associates (塔利班), 和
others simply deemed to be troublemakers in the neighborhood (伊拉克). 那里
was debate in the United States over the strategic wisdom of invading Iraq, 但
none of Saddam Hussein’s crimes—either known, suspected, or fabricated—
were held to an evidentiary standard even close to certainty.53 States that con-
sider giving nuclear weapons to terrorists cannot be certain how the victim
will react, but basing one’s hope for survival on a victim’s reluctance to act on
partial evidence of culpability would be a tremendous gamble.
A nuclear terror strike would have momentous consequences. In the case of
an attack on the United States, such a strike would draw the full investigative,
外交, and military might of the world’s only superpower. In that environ-
蒙特, the incentives for allies, neutrals, and adversaries to cooperate would be
immense. 所以, the data offered in ªgures 1 到 3 (which show attribution
rates after attacks that are, by comparison to a nuclear event, mere pinpricks)
probably greatly underestimate the odds of attribution. Uncertainties about the
full list of possible accomplices might endure, but the notion that a victim of a
nuclear terrorist attack would be paralyzed by those uncertainties is far-fetched.
结论
President Obama has identiªed nuclear terrorism as “the single biggest threat
to U.S. 安全,” describing it as “something that could change the security
landscape of this country and around the world for years to come.”54 The pros-
pect of an adversary state covertly giving a nuclear weapon or nuclear materi-
als to a terrorist organization has been the animating force in U.S. 盛大
strategy for more than a decade. The scenario was used to justify the invasion
of Iraq and toppling of the Iraqi regime in 2003; 并在 2012 和 2013, propo-
nents of a preventive military strike on Iran’s nuclear facilities frequently ar-
gued that such attacks are necessary to eliminate the possibility of Iran trying a
53. 例如, according to Lawrence Wright’s authoritative account, the Taliban was not
complicit in the planning of the September 11 attacks. 赖特, The Looming Tower: Al-Qaeda and the
Road to 9/11 (纽约: 优质的, 2006).
54. 巴拉克奥巴马, speech given at the Nuclear Security Summit, 华盛顿, 华盛顿特区, 四月 10,
2010.
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国际安全 38:1 104
nuclear attack by proxy against Israel or the United States. We demonstrate
here that such fears are overblown. The rationale for state sponsorship of nu-
clear terrorism lacks sound deductive logic and is empirically unsupported by
the most relevant available evidence.
The United States and its allies should be able to deter nuclear-armed states
from passing their weapons to terrorists, because a terrorist nuclear strike
would not remain anonymous for long and would soon be traced back to the
originating state. This conclusion is based on two empirical ªndings. 第一的,
among the relevant past cases of conventional terrorist attacks—those targeting
the homelands of powerful states and causing signiªcant casualties—almost all
were successfully attributed to the perpetrating terrorist organization. 第二,
linking the attributed terrorist organization to a state sponsor would not be
difªcult. Few foreign terrorist organizations have state sponsors; those that do
typically have only one; and only one suspected state sponsor of terrorism
(巴基斯坦) has nuclear weapons or sufªcient stockpiles of nuclear materials.
此外, potential sponsors of nuclear terror face a wicked dilemma:
to maintain distance by passing the weapon to a terrorist group they do not
know well or trust, or to maintain control by giving it to a group they have co-
operated with repeatedly. The former strategy is mind-bogglingly dangerous;
the latter option makes attribution from terror group to sponsor simple.
Our ªndings have two important policy implications. 第一的, the fear of nu-
clear attack by proxy by itself does not justify costly military steps to prevent
nuclear proliferation. Nuclear proliferation may pose a variety of other risks,
and the appropriate level of U.S. efforts to stop proliferation should depend on
the cumulative effect of these risks, but the dangers of a nuclear handoff to ter-
rorists have been overstated. 例如, Iranian leaders would have to be
crazy or suicidal to think that they could give a nuclear weapon to one of their
terrorist collaborators and face no repercussions. If leaders were that irrational,
the bigger problem would be direct nuclear attack without concern for the
retaliatory consequences, not the alleged problem of a nuclear handoff.
A second implication is that instead of publicly stressing the dangers of
nuclear attack by proxy and lamenting the limits of U.S. nuclear forensic capa-
能力 (and thus potentially misleading enemies to overestimate the feasibility
of an anonymous attack against America), the United States should be adver-
tising its impressive record of attributing highly lethal terrorist attacks. 在下面-
stating one’s own capabilities is a reasonable strategy for luring an enemy into
making an unwise attack, but it is a disastrous policy if the goal is deterrence.
The most effective way to deter countries from passing weapons to terrorists is
to demonstrate the ease of nuclear attribution and the devastating conse-
quences of such attribution to the sponsoring state.
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