State-Sponsored Nuclear Proliferation: Why States Share Nuclear Weapons Technology


State-sponsored nuclear proliferation, defined as a government’s intentional assistance to another state to acquire the means of producing nuclear weapons, including the transfer of weapons-grade fissile material, the technology to produce weapons-grade fissile material, or warhead design information, has had a crucial influence on the spread of nuclear weapons. The nuclear warhead design supplied to Libya by the Pakistani scientist A.Q. Khan was initially obtained from China which was itself the recipient of extensive nuclear assistance from the Soviet Union. Iraq, Libya, and Syria might have become members of the nuclear club thanks to sensitive nuclear assistance from other states if outside intervention had not stopped their programs. The current nuclear crises with Iran and North Korea were triggered by the transfer of uranium enrichment technology from Pakistan. Iran is now offering to engage in ostensibly peaceful nuclear cooperation with countries such as Algeria, Nigeria, Sudan, and Venezuela.

The motivations behind this type of proliferation are an unsolved puzzle. Why do states share nuclear weapons technology—the most powerful military technology ever invented—with other states? The anarchic nature of international relations and the destructive power of nuclear weapons suggest that this type of cooperation should be rare. And yet states have engaged in nuclear weapon cooperation since the dawn of the atomic age. The first instance of such nuclear sharing was Anglo-American cooperation on the Manhattan Project during World War II. North Korea’s assistance to Syria’s nuclear reactor project, which was destroyed by an Israeli airstrike in 2007, is the most recent example of this phenomenon. As part of my research on state-sponsored proliferation, I have documented over a dozen cases of states sharing nuclear weapon technology with another state.

Surprisingly, state-sponsored nuclear proliferation, which has profound implications for U.S. nonproliferation policy and international security, has received a fraction of the attention devoted to understanding why states develop1, forgo2, or abandon3 nuclear weapon programs. A recent two-volume study on the future of nuclear proliferation focused entirely on the demand-side of proliferation and neglected the role of states as suppliers of nuclear weapons technology.4

The question of why states share nuclear weapons technology and the security implications of such transfers has been examined largely on a case-by-case basis with little attention paid to theory or comparisons across cases. Early studies on nuclear weapon cooperation were speculative in nature since they lacked any empirical evidence and were not informed by theoretical considerations.5 The second generation of studies examined nuclear cooperation on a case-by-case basis, again without a theoretical framework.6 Only recently have political scientists engaged this question from a theoretical perspective with the support of empirical evidence.7 Even this most recent scholarship suffers from some shortcomings. First, it is too reliant on quantitative methods that do not provide insights into the causal mechanisms behind a government’s decision to assist, and sometimes terminate, nuclear assistance.8 Second, it draws on a narrow slice of international relations theory, primarily neorealism, to explain cases of nuclear cooperation. Matthew Kroenig, for examples, relies on balance of power and deterrence theory to construct his strategic theory of sensitive nuclear assistance which focuses on whether or not the proliferating state has the ability to project power against the recipient state.9 According to Kroenig, states are more willing to provide sensitive nuclear assistance to states that they do not have the ability to project power against. While this may be a permissive factor in state-sponsored nuclear proliferation, it is not a proximate cause of such behavior. Third, the literature is biased in that it examines only cases where such nuclear cooperation occurred. There are also a number of “near misses” (cases where states explored the option of cooperating on nuclear weapon programs but didn’t proceed) that shed light on the relative influence of different causal factors on such decisions. While the literature on state-sponsored nuclear proliferation has improved markedly in recent years, there are still large gaps in the empirical record. The motivations and casual mechanisms driving this behavior also remain murky.

My research seeks to advance our understanding of this phenomenon by drawing on a wider array of theories to explain why states share nuclear weapon technologies and providing more detailed case studies to better explain specific cases and highlight the relative influence of different causal mechanisms. This project utilizes three models—the national security model, the parochial interest model, and the cultural model—to explain why states share the technology to build nuclear weapons with other states. This three-fold theoretical framework provides the foundation for a systematic, comparative analysis of the motivations behind state-sponsored nuclear proliferation. The national security model is based on neorealism which posits that in order to survive in an anarchic international system states must arm themselves or ally with other states for protection against external threats.10 Under this model, states engage in nuclear weapon cooperation for strategic purposes such as countering a shared enemy, to avoid an extended deterrence commitment, or to obtain vital military resources. The parochial interest model, based on liberal international relations theory, emphasizes the role of domestic sub-national actors, such as the military and the nuclear energy establishment, whose objectives are to maximize their private gains.11 These actors engage in nuclear cooperation as a means of increasing their power, autonomy, and/or prestige. According to the cultural model, based on constructivism, the decision to provide sensitive nuclear assistance is a function of shared beliefs and identities, including religion and ideology, not necessarily what is in the national interest or best serves the material interests of decision-makers.12

It should be noted that none of the cases of nuclear sharing uncovered to date can be explained wholly by any single model. Indeed, different models may have greater explanatory power at different phases of nuclear cooperation. Also, the motivations of the state providing the nuclear technology and the state receiving it may be different. Nonetheless, these models serve a practical purpose in differentiating the alternative causes of nuclear sharing and highlighting the conditions that lead to its initiation, continuation, and termination. This holistic approach is in line with what Peter Katzenstein has dubbed analytic eclecticism. According to Katzenstein, “The complex links between power, interest, and norms defy analytical capture by any one paradigm. They are made more intelligible by drawing selectively on different paradigms—that is, by analytical eclecticism, not parsimony.”13

The heart of the project is a series of case studies designed to illustrate the strengths and weaknesses of the national security, parochial interest, and cultural models. These cases are analyzed through a combination of process tracing, which traces the links between possible causes and observed outcomes within cases, and structured, focused comparison which applies a standardized set of general questions across cases.14 The method of process tracing is well-suited to identifying the relative importance of different causal factors in a government’s decision-making process and establishing the internal validity of a case study. The structured, focused comparison method is valuable for testing the validity of the three models across different cases and providing a basis on which to make generalizable findings. Cases have been selected for their historical importance, richness of primary and secondary sources, ability to test the explanatory power of the three different models, and policy relevance. For example, the most common version of the cultural explanation for state-sponsored nuclear proliferation is the “Islamic bomb”: the belief that a Muslim state would share nuclear weapon technology with other states sharing its religious identity. The case of Pakistani-sponsored nuclear proliferation presents an important test of the cultural model. Pakistan, the only Muslim-majority state with nuclear weapons, has transferred uranium enrichment technology to three states: Iran, Libya, and North Korea. Thus, it is important to determine to what extent was Pakistan’s proliferation motivated by shared religious identity versus national security concerns or the greed of a rogue scientist. The history of state-sponsored nuclear proliferation is also characterized by several cases, such as Anglo-American cooperation during and after World War II, Sino-Soviet cooperation in the 1950s, and Franco-Israeli cooperation in the 1950s, where the donor had second thoughts and terminated its nuclear assistance prematurely. Such cases are particularly useful for capturing within-case variance among the different causal factors and providing insights into why states initiate and terminate nuclear cooperation.

State-sponsored nuclear proliferation presents not only an intriguing puzzle for international relations theory, but also a pressing challenge to policy-makers. In order to devise effective nonproliferation strategies, policy-makers need to understand what factors motivate states to share nuclear weapon technology and under what conditions such cooperation is more or less likely to take place. This project will provide policy-makers with a richer historical and theoretical context with which to view current and future cases of state-sponsored nuclear proliferation. For example, this project will provide a framework for analyzing the risk that Iran would provide sensitive nuclear assistance to other states. The study will also delineate the different types of nuclear weapon assistance that states have pursued and received and how the type of assistance influences the timing and trajectory of nuclear weapon programs. This analysis will also shed light on whether government-supplied nuclear assistance poses special challenges to intelligence collection and analysis compared to other proliferation pathways. The impact of state-sponsored nuclear proliferation on crisis stability, deterrence, and the risks of preventive military action will also be explored. The three models used in this project can also be used to analyze the potential motives for a state to transfer fissile material or nuclear weapons to a terrorist group. Since an event of this kind has never occurred it is necessary to study the closest analog to such behavior. Understanding what has motivated and deterred states from sharing nuclear technology with other states will further the debate on the risk of state-sponsored nuclear terrorism. Overall, these contributions will enable policy-makers to develop more effective strategies for halting nuclear proliferation and strengthening nuclear security.


  1. Scott Sagan, “Why Do States Build Nuclear Weapons? Three Models in Search of a Bomb,” International Security, Vol. 21, No. 3 (Winter 1996/97), pp. 54-86. []
  2. T.V. Paul, Power Versus Prudence: Why Nations Forgo Nuclear Weapons (Montreal: McGill-Queen’s University Press, 2000). []
  3. Ariel Levite, “Never Say Never Again: Nuclear Reversal Revisited,” International Security, Vol. 2, No. 3 (Winter 2002/03), pp. 59-88. []
  4. William C. Potter and Gaukhar Mukhatzhanova, eds., Forecasting Nuclear Proliferation in the 21st Century, 2 Vols. (Stanford: Stanford University Press, 2010). []
  5. Lewis A. Dunn, “Nuclear “Gray Marketeering”,” International Security, Vol. 1, No. 3 (Winter 1977), pp. 107-118. []
  6. Jason D. Ellis, “Beyond Nonproliferation: Secondary Supply, Proliferation Management, and U.S. Foreign Policy,” Comparative Strategy, Vol. 20, No. 1 (January-March 2001), pp. 1-24; T.V. Paul, “Chinese-Pakistani Nuclear/Missile Ties and Balance of Power Politics,” The Nonproliferation Review, Vol. 10, No. 2 (Summer 2003), pp. 21-29; Peter Liberman, “Israel and the South African Bomb,” The Nonproliferation Review, Vol. 11, No. 2 (Summer 2004), pp. 1-35; Chaim Braun and Christopher F. Chyba, “Proliferation Rings: New Challenges to the Nuclear Nonproliferation Regime,” International Security, Vol. 29, No. 2 (Fall 2004), pp. 5-49; Andrew J. Coe, “North Korea’s New Cash Crop,” The Washington Quarterly, Vol. 28, No. 3 (Summer 2005), pp. 73-84; and David Albright, Peddling Peril: How the Secret Nuclear Trade Arms America’s Enemies (New York: Free Press, 2010). []
  7. Matthew Kroenig, Exporting the Bomb: Technology Transfer and the Spread of Nuclear Weapons (Ithaca: Cornell University Press, 2009); Matthew Kroenig, “Exporting the Bomb: Why States Provide Sensitive Nuclear Assistance,” American Political Science Review, Vol. 103, No. 1 (February 2009), pp. 113-133; Matthew Kroenig, “Importing the Bomb: Sensitive Nuclear Assistance and Nuclear Proliferation,” Journal of Conflict Resolution, Vol. 53, No. 2 (April 2009), pp. 161-180; and Matthew Fuhrmann, “Spreading Temptation: Proliferation and Peaceful Nuclear Cooperation Agreements,” International Security, Vol. 34, No. 1 (Summer 2009), pp. 7–41. []
  8. Kroenig, “Exporting the Bomb”; Kroenig, “Importing the Bomb”; and Fuhrmann, “Spreading Temptation.” []
  9. Kroenig, Exporting the Bomb, pp. 10-49. []
  10. Kenneth Waltz, Theory of International Politics (New York: McGraw Hill, 1979). []
  11. Andrew Moravcsik, “Taking Preferences Seriously: A Liberal Theory of International Politics,” International Organization, Vol. 51, No. 4 (Autumn 1997): 528-530. []
  12. Peter J. Katzenstein, ed., The Culture of National Security: Norms and Identity in World Politics (New York: Columbia University Press, 1996). []
  13. Peter J. Katzenstein and Nobuo Okawara, “Japan, Asia-Pacific Security, and the Case for Analytical Eclectism,” International Security, Vol. 26, No. 3 (Winter 2001/02), p. 154. []
  14. Alexander L. George and Andrew Bennett, Case Studies and Theory Development in the Social Sciences (Cambridge, MA: MIT Press, 2005). []


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