1) "The Determinants of Nuclear Force Structure” with Erik Gartzke and Jeffrey Kaplow. Journal of Conflict Resolution, April 2014.
Reprinted in Nonproliferation Policy and Nuclear Posture: Causes and Consequences for the Spread of Nuclear Weapons, edited by Neil Narang, Erik Gartzke, and Matt Kroenig. Routledge Press, 2015.
A substantial literature examines the causes of nuclear proliferation, but few studies have addressed why states decide on a particular portfolio of weapons systems once they have acquired a basic nuclear capability. We advance a portfolio theory of nuclear force structure, positing that states seek a diverse set of capabilities for nuclear deterrence, but that they also face major resource and organizational constraints. A number of factors may help to explain the portfolio of nuclear forces that states ultimately field, including resource availability, experience as a nuclear power, bureaucratic politics, the conventional threat environment, the presence of nuclear rivals, and the maintenance of nuclear alliances. We test the influence of these factors on force structure using a new dataset of nuclear weapons platforms fielded by nine nuclear nations between 1950 and 2000. Our findings represent an important step in understanding the drivers of nuclear behavior after states have joined the nuclear weapons club.
2) “The Unforeseen Consequences of Extended Deterrence: Moral Hazard in a Nuclear Protégé” with Neil Narang, Accepted at the Journal of Conflict Resolution.
Do “nuclear umbrellas” create a moral hazard that can increase the risk of war? In this paper, we investigate whether situations of extended deterrence in which a nuclear patron makes a defensive commitment to a non-nuclear client state can inadvertently increase the likelihood that a client will initiate a crisis with another state. Using data on the crisis behavior of states from 1950-2000, we estimate the impact of a nuclear umbrella on various crisis outcomes, including the initiation and escalation of militarized conflict. Interestingly, we find no evidence that such commitments increase the risk of war or even two-sided violence at lower levels. However, consistent with both the moral hazard logic and bargaining theories of war, we show that this appears to be because potential target states offer increased policy concessions to client states to avoid costly fighting. Thus the link between nuclear umbrellas and moral hazard appears to be real, but it is reflected in the division of benefits rather than a greater likelihood of war. The results have important policy implications as the US contemplates extending its nuclear umbrella.
3) “Benefits and Burdens of Nuclear Latency” with Rachel Whitlark, Forthcoming at International Studies Quarterly.
How does the acquisition of latent nuclear capabilities in the form of enrichment and reprocessing facilities affect a state’s military security and bargaining power? On the one hand, nuclear latency might serve as a “virtual deterrent” against would-be aggressors and as a bargaining chip in international negotiations. On the other hand, this idea conflicts with research demonstrating that states cannot deter military challenges without at least a deliverable nuclear device, and to scholarship suggesting that a state’s pursuit of latency invites nonproliferation sanctions and preventive strikes. This paper addresses this debate by quantitatively investigating the conditions when latency benefits or burdens states in their international interactions. To do so, it analyzes a revised dataset of latency measures and a variety of military and bargaining outcomes. The results suggest that latency invites coercion without producing deterrence, a finding with implications for U.S. nonproliferation policy and the broader literature on nuclear weapons.
4) “Windows of Opportunity: Nuclear Reversal and Leadership Change”
This paper examines the critical role of the international community in influencing nuclear reversal decisions and whether the emergence of new leaders can facilitate an agreement. The theoretical analysis suggests that rewards play an important information-gathering and coercive role in persuading proliferators to stop their programs, while the imposition of economic sanctions may be less effective. Further, the theory also suggests that rewards are more useful when offered to new leaders in proliferating states. Using data on all nuclear weapons activity from 1945-2007, this articles tests these hypotheses on leader change and international inducements. The analysis reveals that upon the introduction of new leaders, political and military rewards are associated with an increase in the probability of nuclear reversal, while the use of economic sanctions may reduce the likelihood that a state will reverse its program. This analysis also demonstrates that the association between military assistance and nuclear reversal attenuates and reverses once a leader remains in power more than three years. The article concludes with a closer examination of policy levers that the international community can use to alter proliferation behavior.
5) “Assurance and Deterrence in a Cross-Domain World,” (under review at Oxford University Press)
With the advent of new capabilities for combat, the nature of international relations has become increasingly complex and intertwined. Conflicts and crises are no longer fought in isolation and states often rely on friends and allies to assist in war fighting. In today’s international environment, capable states can project power and deploy troops, resources, and sophisticated technologies to distant allies with relative ease. Indeed, with the introduction of new capabilities that intersect existing military domains with emerging arenas of non-kinetic conflict in cyber or space, it becomes critical to analyze how this evolution impacts the relationship between United States and its allies in the international system. In this chapter, I explore US foreign policy in the context of its international commitments and the supply and demand market for defense. Specifically, this article examines historical US commitments to assure and protect allied partners and to deter aggression, and how these polices have evolved since World War II with increased investment and development of new kinetic capabilities, including the enhancement of the US nuclear arsenal with the introduction of long-range and sea-based capabilities. This theoretically driven historical analysis uses specific cases from the World War II and Cold War eras to provide a useful backdrop for assessing modern-day extended deterrence in a cross-domain system. Using this framework, I engage current discussions in the policy and military communities to discuss how the United States can leverage its recent development of capabilities to reassure existing allies and potentially expand the umbrella to additional allies seeking the deterrent capabilities of the United States. I conclude with a broader discussion of the policy implications of how strategies of extended deterrence, and the market for capabilities-based alliances, will continue to shift and evolve in an increasingly cross-domain system.
6) “Deterrence and the Structure of Nuclear Forces,” with Erik Gartzke and Jeffrey Kaplow, under review.
Deterrence theory emphasizes that nations with nuclear weapons should be less likely to fight. But which nations and under what circumstances? Conceptions of what constitutes an adequate nuclear deterrent vary from possession of the bomb, to large(r) nuclear arsenals, to secure ``second-strike'' capabilities. We develop and analyze data that allows us to distinguish between these different alternatives. We further differentiate between the effects of nuclear capabilities on potential initiators and possible targets of attack. States with nuclear weapons initiate more conventional disputes than non-nuclear nations, but are also less likely to be targeted by other countries than are non-nuclear states. This distinction has not been widely recognized in the literature and helps to account for the tentative and contested nature of existing evidence. We show that the proliferation of weapons platforms---a key component of nuclear force structures contributing directly to second-strike security---and not arsenal size or nuclear status, makes nuclear states both more likely to initiate and less likely to be targets of conventional conflict.
7) “The Determinants of Nuclear Latency,” with Rachel Whitlark.
Why do states construct facilities for producing fissile material? Past studies of states’ nuclear decisions primarily addressed the determinants of nuclear weapons programs. Recent scholarship has moved beyond this debate by examining the steps along the proliferation pathway, especially the acquisition of technologies such as uranium enrichment and plutonium reprocessing (ENR), which enable states to achieve “nuclear latency.” But while researchers have investigated the international consequences of ENR proliferation, they have yet to examine its causes. This paper fills that gap in the existing literature by investigating whether states that constructed ENR facilities did so primarily to facilitate the nuclear weapons option, or whether latency was merely the byproduct of commercial needs. To pinpoint states’ motivations, this paper employs a combination of statistical and historical approaches. On the quantitative side, it uses revised time-series data on national ENR capabilities, together with data on economic and military characteristics, to assess the correlates of ENR acquisition. On the qualitative side, it employs detailed case studies of Japan, South Korea, Argentina, and Egypt to establish the motivations for ENR programs. The paper concludes by deriving the implications of this research for international security and U.S. foreign and nuclear policy.
8) “The Determinants of Nuclear Reversal,”Featured in the Monkey Cage (Washington Post)
This paper examines the critical role of the international community in influencing nuclear reversal decisions. Analysis of the formal theory reveals rewards play an important information gathering and coercive role in persuading all types of proliferates to stop their programs. Further, the model suggests that, while the use of sanctions is generally employed against persistent proliferators, it is likely to be unsuccessful in persuading them to stop their pursuit. Using data on all nuclear weapons activity from 1945-2007, this articles tests these hypotheses using a spectrum of positive and negative inducements. The analysis reveals that political and military rewards are associated with an increase in the probability of nuclear reversal, while the use of economic sanctions may reduce the likelihood that a state will reverse its program. The article concludes with a closer examination of policy levers that the international community can use to alter proliferation behavior.
9) Resolving Uncertainty: How Lower Costs of Nuclear Weapons Can Cause Less Proliferation
How does changing the costs of proliferation change the likelihood of nuclear proliferation? We develop a model in which a country offers concessions to a would-be proliferator to convince the latter to not acquire nuclear weapons. However, the country faces uncertainty over the proliferator's resolve. In equilibrium, if the proliferator has a credible threat to build nuclear weapons, higher costs of weapons cause an increase in the probability of proliferation. This counterintuitive effect arises because higher costs exacerbate the proposer's information problem. Equivalently, lower costs of nuclear weapons solve the proposer's information problem and increase the probability of a negotiated settlement. We trace the mechanism by exploring the United States' attempt to compel Pakistan from acquiring nuclear weapons. Despite facing immense technological hurdles, Pakistan nevertheless developed a nuclear weapon after the United States proposed offers designed only to achieve compliance if Pakistan's resolve were low.