Signing Away the Bomb: The Surprising Success of the Nuclear Nonproliferation Regime

2022. Cambridge University Press.

For more than fifty years, the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) and the wider nuclear nonproliferation regime have worked to prevent the spread of nuclear weapons. Analysts and pundits have often viewed the regime with skepticism, repeatedly warning that it is on the brink of collapse, and the NPT lacks many of the characteristics usually seen in effective international institutions. Nevertheless, the treaty continues to enjoy near-universal membership and high levels of compliance. This is the first book to explain why the nonproliferation regime has been so successful, bringing to bear declassified documents, new data on regime membership and weapons pursuit, and a variety of analytic approaches. It offers important new insights for scholars of nuclear proliferation and international security institutions, and for policymakers seeking to strengthen the nonproliferation regime and tighten international constraints on the spread of nuclear weapons.

The Changing Face of Nuclear Proliferation

2024. International Studies Quarterly.

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  A rich literature has identified a number of important drivers of nuclear proliferation. Most of this work, however, treats the determinants of proliferation as constant over the entire nuclear age—the factors leading to proliferation are assumed to be the same in 2010 as they were in 1945. But there are reasons to suspect that the drivers of proliferation have changed over this time: nuclear technology is easier to come by, the global strategic environment has shifted, and the nuclear nonproliferation regime has come into being. To examine changes in the dynamics of nuclear proliferation, I adapt a cross-validation technique frequently used in the machine learning literature. I create a rolling window of training data with which statistical models of proliferation are built, and I then test the predictive power of these models against data from other time periods. The result of this analysis is a temporal map of how the determinants of proliferation have changed over time. My findings suggest that the underlying dynamics of nuclear proliferation have indeed shifted, with important implications both for the literature on nuclear proliferation and for policymakers interested in limiting the future spread of nuclear weapons.

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State Compliance and the Track Record of International Security Institutions: Evidence from the Nuclear Nonproliferation Regime

2022. Journal of Global Security Studies.

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  Why do states choose to comply with international security institutions, and what factors drive changes in compliance behavior over time? This article argues that these institutions are based on a fundamental bargain among members—each is willing to comply only so long as others do—but there is often uncertainty about the compliance of others. The track record of the institution provides information that helps to resolve this uncertainty. As time passes with few violations, states will be more likely to comply themselves; evidence of increasing noncompliance, on the other hand, will make states more likely to cheat. Analysis of data on nuclear weapons programs from 1968 to 2010 finds that members of the nuclear nonproliferation regime are more likely to pursue nuclear weapons when there have been a greater number of recent violations of the regime. These findings point to a more dynamic view of international security institutions than has generally been recognized in the literature.

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The Determinants of Uncertainty in International Relations

2021. International Studies Quarterly. With Erik Gartzke.

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  Uncertainty about military power is widely considered an important determinant of international conflict, but research in international relations provides relatively little guidance about the origins of uncertainty. What factors influence the validity of actors’ assessments of military capabilities? When would one expect uncertainty about military capabilities to be particularly high, or especially low? We examine a series of factors capable of explaining the sources of uncertainty in international relations, positing that the uncertainty of assessments is a function of both characteristics of the state being assessed and the overall strategic environment. We test our theory using new measures of uncertainty that we derive from analyzing publicly available estimates of national military capabilities. Our findings offer a novel set of implications both for research that relies on uncertainty as a key cause of conflict and for policymakers faced with evaluating foreign military assessments.

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The Negotiation Calculus: Why Parties to Civil Conflict Refuse to Talk

2016. International Studies Quarterly.

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  Why do some parties to intrastate conflict refuse to negotiate? I propose a simple theory of civil conflict in which the act of negotiation itself carries costs and benefits. Several hypotheses follow: parties to civil conflict will avoid negotiation when they (1) fear alienating external supporters or internal constituencies, (2) risk granting legitimacy to their opponents or signaling weakness to other potential claimants, or (3) find it difficult to identify reliable negotiating partners. Empirical tests find support for my argument. My findings suggest that cases exist in which the parties would reach an agreement if only they could overcome the costs of negotiation and engage in talks. Diplomats and mediators should consider the costs and benefits of talks when planning the timing and form of interventions designed to bring parties to the table.

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The Canary in the Nuclear Submarine: Assessing the Nonproliferation Risk of the Naval Nuclear Propulsion Loophole

2015. Nonproliferation Review.

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  The Treaty on the Non-Proliferation of Nuclear Weapons (NPT) allows states to exempt nuclear material from international safeguards for use in nuclear submarine programs. This material, however, could be diverted for nuclear weapons purposes without the knowledge of inspectors, creating a potentially dangerous loophole in the treaty. This paper argues that to exercise the loophole today would amount to admitting a nuclear weapons program, making it a particularly poor pathway to a weapon for a potential proliferant. Still, if states like Brazil ultimately exempt nuclear material from safeguards for a nuclear submarine effort, they could set a dangerous precedent that makes it easier for others to use the loophole as a route to a nuclear weapons capability. There are several policy options available to mitigate the damage of such a precedent; most promising is the prospect of a voluntary safeguards arrangement that would allow international inspectors to keep an eye on nuclear material even after it has been dedicated to a naval nuclear propulsion program.

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The Days After a Deal with Iran: Implications for the Nuclear Nonproliferation Regime

2015. RAND Perspective. With Rebecca Davis Gibbons.

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  This analysis begins by positing that a nuclear agreement is reached between Iran and the United States, Great Britain, France, Russia, China, and Germany (P5+1). One of a series of RAND perspectives on what the Middle East and U.S. policy might look like in “the days after a deal,” this Perspective examines the deal’s implications for the nuclear nonpro- liferation regime. A completed deal with the Iranians represents good news for the nuclear nonproliferation regime overall. An agreement will reassure some states about the effectiveness of the regime and could contribute to stronger IAEA safeguards in the future, offering inspectors a better chance of detecting undeclared nuclear activities. At the same time, however, an agreement will almost certainly allow Iran to maintain a uranium enrichment capability. This may tempt some states to expand their nuclear infrastructure as part of a hedging strategy. A nuclear agreement with Iran also effectively legitimizes a domestic nuclear infrastructure that was built despite Iran being found in noncompliance with its agreements under the NPT. These downsides to a deal could pose additional challenges to the credibility of the nuclear nonproliferation regime and potentially ease the path for nuclear pursuit by other states in the future.

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Talking Peace, Making Weapons: IAEA Technical Cooperation and Nuclear Proliferation

2014. Journal of Conflict Resolution. With Robert L. Brown.

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  A growing literature suggests that nuclear assistance from other countries is an important determinant of whether states pursue nuclear weapons. Existing work does not consider, however, the most widely available source of assistance—the Technical Cooperation (TC) program administered by the International Atomic Energy Agency (IAEA). IAEA assistance is an important piece of the nonproliferation regime’s central bargain: member states enjoy nuclear assistance in exchange for agreeing not to seek nuclear weapons. Using a dataset of TC projects since 1972, we examine whether international nuclear assistance is associated with the pursuit of nuclear weapons. We hypothesize that some TC assistance reduces the cost of pursuing nuclear weapons, making weapons programs more likely. We find that receiving TC related to the nuclear fuel cycle is a statistically and substantively significant factor in state decisions since 1972 to seek nuclear weapons, with important implications for existing theories of nuclear proliferation.

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The Determinants of Nuclear Force Structure

2014. Journal of Conflict Resolution. With Erik Gartzke and Rupal N. Mehta.

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  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.

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Who Shall I Say Is Calling? Signal Sender Uncertainty in International Diplomacy

With Marcus Holmes.

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  Problems of signaling are ubiquitous and well documented in international politics, but most of the literature focuses on the “cheap talk” nature of signals. Less well recognized is the class of signal sender uncertainty problems, in which the sender of a signal cannot be easily authenticated. These cases often involve diplomatic intermediaries or emissaries. In this paper, we propose a simple typology that identifies two key factors driving the level of signal sender uncertainty in diplomatic communications: trust in intermediaries and the consistency of the signal. We offer several examples of signal sender uncertainty drawn from past diplomacy, showing that signal sender uncertainty will be most evident when both trust in the intermediary and consistency of the signal are low; in these cases, even legitimate signals are unlikely to be taken seriously by their intended recipient. This finding has important implications for policymakers, and we discuss a number of potential mechanisms for reducing uncertainty and facilitating effective diplomatic communications.

Distributed Ledger Technology and Nuclear Safeguards

With Tara McLaughlin and Troy Wiipongwii.

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  Nuclear safeguards are a central pillar of international nuclear nonproliferation efforts. Teams of international inspectors—primarily, but not exclusively, from the International Atomic Energy Agency (IAEA)—routinely visit nuclear facilities worldwide to verify that no nuclear material has been diverted from civilian power plants to nuclear weapons efforts. Inspectors engage in material accounting, measuring nuclear materials that enter a facility and comparing those measurements with a facility’s output. This task is complicated, however, by a number of factors, including routine changes to nuclear process lines, adversarial relationships with host countries, incentives to minimize the disruptions caused by inspectors while on site, and, of course, real efforts by governments to divert material for a bomb without alerting inspectors. The structure of international nuclear safeguards seems a natural fit for distributed ledger technology (DLT). The primary task of inspectors is to maintain a kind of ledger, identifying nuclear inputs and outputs. The ability to securely and verifiably make changes to a distributed ledger offers a number of potential benefits to inspectors, to nations interested in making safeguards more effective, and to host countries looking to minimize the cost and effort of the safeguards regime. Like any new safeguards technology, however, there are substantial barriers to acceptance of DLT both by the IAEA and states that are subject to international inspection.

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Deterrence and the Structure of Nuclear Forces

With Erik Gartzke and Rupal N. Mehta.
Presented at the 2020 APSA Annual Meeting.

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  Nuclear weapons are said to deter through the threat of a punishing retaliatory “second strike.” To do so, a sufficient portion of a nation’s nuclear capabilities must survive initial enemy attack. We examine the conventional security implications of conditions that enhance survivability, or that alternately threaten the security of nuclear powers. Diversifying nuclear delivery platforms is “deterrence dominant” in that it increases the survivability of nuclear forces without adding to the destructiveness of a first strike. In contrast, increasing the number of warheads per delivery platform augments the offense without much improving deterrence. Other features of nuclear force structures, such as the total number of warheads or delivery systems, or the presence of ballistic missile submarines or a nuclear “triad,” have much weaker or varying effects on deterrence, since they affect both the first and second strike. We confirm our theoretical claims in statistical tests using recently compiled data of nuclear force structures for all nuclear dyads. We provide a variety of robustness checks of our findings and discuss ways to improve stability.

Assessing Proliferation Risk: Using Data Analytics to Evaluate Emerging Nuclear Threats

Presented at the 2019 ISSS-IS Conference.

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  The nuclear proliferation landscape has changed. Twenty years ago, the countries most likely to seek nuclear weapons were easily identified, and the factors that could push them into nuclear pursuit were well understood. Today, widespread latent capability has made the list of countries with the capacity for weapons pursuit much longer, and the potential triggers for nuclear proliferation have grown more complex. To deal effectively with today’s nuclear proliferation threats, intelligence and policy analysts need versatile tools to evaluate proliferation risk and focus limited resources and analytic capacity. This article employs the tools of data science to develop a new measure of the likelihood that a country will seek nuclear weapons under particular circumstances: the proliferation risk score. Proliferation risk scores are both scalable and flexible. They can be updated with new data and expanded to cover new factors that might lead to nuclear pursuit, and they can be used in a variety of what-if scenarios to identify factors that represent the greatest risk for a specific country in a specific global situation. They can be helpful to analysts as an adjunct to traditional analysis and as a starting point for structured analytic approaches.

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Changing Pathways to a Bomb

Presented at the 2019 APSA Annual Meeting.

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  While a large literature has theorized about the decision of states to develop nuclear weapons, few scholars examine pathways to a weapon—how states actually go about building a bomb. The conventional wisdom has been that states subject to nuclear safeguards would use undeclared, secret facilities to produce the highly enriched uranium or plutonium necessary for nuclear weapons. The example of Iran, however, suggests that this view may need to be reevaluated. I theorize that broad changes in nuclear proliferation dynamics make would-be proliferants more likely to pursue a latent nuclear capability—acquiring technology that brings them just to the edge of having a nuclear weapon—than to pursue a covert weapons effort. My findings have important implications for the international community’s efforts to limit the spread of nuclear weapons technology in the future.

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The Determinants of Multilateral Nuclear Assistance

With Robert L. Brown.
Presented at the 2017 ISA Annual Convention and 2013 MPSA Annual Conference.

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  The International Atomic Energy Agency (IAEA) is the world’s foremost provider of nuclear assistance, but its contribution is often overlooked by the existing literatures on nuclear proliferation and international organizations. IAEA nuclear assistance is both important in its own right as a potential factor in the proliferation of sensitive nuclear technology, and as a new domain through which to understand how benefits are provided by other international organizations, such as international financial institutions. In this paper, we explore the ways that different principal-agent relationships—as manifested in voting and participation rules, institutional procedures, and other mechanisms of state control—affect the influence of powerful states over the distribution of multilateral assistance. We test our theories using a dataset of all IAEA nuclear assistance projects since 1971. Our findings have important implications for theoretical work on delegation and agency in international organizations, as well as the literature on the drivers of nuclear proliferation. We also offer new points of leverage for policymakers seeking to limit the spread of sensitive nuclear technology.

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Testing the Role of Uncertainty in Conflict

With Erik Gartzke.
Presented at the 2015 ISA Annual Convention, the 2014 Empirical Implications of Bargaining Models (EIBM) workshop, and the 2013 APSA Annual Meeting.

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  Bargaining theories of international conflict posit that war stems from states’ uncertainty about their rivals’ capabilities or resolve. While theoretically compelling, this model is difficult to test empirically. A direct test of the theory calls for some way to measure a state’s uncertainty about its rival’s capabilities, which has so far eluded international relations scholars. This paper proposes a new measure of state uncertainty, using estimates of states’ military capabilities compiled by non-profit organizations and government agencies. These estimates are often revised as better information becomes available, and the extent to which these estimates change over time is likely to be associated with uncertainty about a state’s capabilities. Using this and related measures of uncertainty, we conduct the first direct tests of whether increased uncertainty is associated with conflict, as bargaining theories of war predict. The findings have important implications for continued efforts to refine rationalist theories of conflict and for our understanding of the underlying causes of war.

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In Search of Nuclear Deterrence: The Effect of Nuclear Weapons Range on International Conflict

With Erik Gartzke and Rupal N. Mehta.
Presented at the 2014 ISA Annual Convention.

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  A vast academic literature has given us a rich theoretical understanding of the effect of nuclear weapons on international conflict, but empirical work on nuclear deterrence has generally yielded weak and often contradictory findings. It thus remains an open question: Do nuclear weapons reduce conventional or nuclear conflict? In this paper, we relax several of the key assumptions made by most quantitative studies of nuclear deterrence—that the arsenals of all nuclear weapons states are equally capable, that all nuclear weapons within a single state have the same capabilities, and that nuclear states can hold every other state at risk with their full arsenal. Most nuclear states also have significant limitations on their ability to project nuclear power beyond their immediate neighborhood, and the threshold for nuclear weapons use may be higher for a state with a handful of weapons than for one with thousands. We build on existing work to develop a theory of nuclear deterrence that takes into account the destructive power that a nuclear state can bring to bear against its adversary. We then test this theory using a new dataset of nuclear forces since 1950 that includes a measure of the range of nuclear weapons. Our findings offer a clearer picture of the role that nuclear weapons play in inviting or limiting international conventional conflict, and have important implications for ongoing policy discussions of nuclear disarmament and changes to nuclear force structures.

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The Nuclear Nonproliferation Regime Complex: A New Dataset

With Shannon Carcelli, Erik Gartzke, and Rebecca Gibbons.
Presented at the 2014 ISA Annual Convention.

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  Scholars wishing to study the impact of international institutions generally examine the characteristics and membership of a single treaty or set of treaties. But rarely does a single treaty—no matter how important—represent the extent of a state’s international commitments in a particular policy realm. Using membership in a treaty as a proxy for regime embeddedness can complicate inference, since there is likely to be much less variation in the membership of a single treaty than there is in the larger regime. In this paper, we introduce a new dataset that maps the nuclear regime—the 43 institutions, treaties, and agreements that deal with arms control and disarmament, nuclear non-proliferation, nuclear testing, and nuclear security. We argue that regime-level data are more appropriate for studies of the role of international institutions in constraining state behavior than are data focused on an individual treaty or treaties. We illustrate the use of the new dataset by developing a new measure of state embeddedness in the nuclear non-proliferation regime, examining whether regime membership has an effect on states’ propensity for conflict. Our data and findings have important implications for the study of international institutions.

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