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Abstract
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.

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.

AbstractWhy 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.

This dissertation examines how international security institutions affect the behavior of states. These institutions seem to defy existing theory: punishment is difficult and information hard to come by, yet security institutions often boast near-universal membership and seem to enjoy high levels of compliance. I argue that these institutions can effectively constrain state behavior because states use the membership and compliance decisions of others as important clues about the efficacy of an institution and about states' underlying policy preferences. I test my hypotheses using data on states' pursuit of nuclear weapons and their membership in the various international agreements that make up the nuclear nonproliferation regime. Chapter 1 summarizes my argument and the contribution of this work to the literature on international organizations and international security. Chapter 2 presents a new theory of compliance in which a state's decision to abide by an international commitment is driven by the track record of the institution---the institution's recent history of compliance. Using data on nuclear weapons programs between 1968 and 2010, my analysis shows 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. In Chapter 3, I argue that deeper security institutions may actually attract more members, because states will only join institutions when they have some reassurance that other member states will comply. I find that states are more likely to join the nuclear nonproliferation regime when various indicators--- verification, enforcement, and compliance---indicate greater depth. Chapter 4 examines selective enforcement within international security institutions. I argue that enforcing states look to the policy preferences of violators when deciding whether to punish their transgressions. I use data on membership in the various agreements that make up the nuclear nonproliferation regime to derive a new measure of state preferences over nonproliferation policy issues, and show that a state's pattern of treaty memberships within the regime significantly affects the likelihood that the international community will pursue costly enforcement measures if the state seeks nuclear weapons

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.

Final Technical Report for PASCC Award #N00244-15-1-0003 An earlier draft of this project was presented at the Annual Meeting of the American Political Science Association, September 2015, San Francisco, CA. ; Researchers have now produced a number of quantitative studies of the determinants of nuclear proliferation, using data on all known nuclear weapons programs. But while scholars have laid important groundwork in understanding the causes of nuclear pursuit, these studies are primarily focused on explaining rather than predicting proliferation. Drawing from existing quantitative work, this project uses statistical learning methods to construct a predictive model of proliferation, focusing on the ability of different nuclear proliferation theories to make accurate out-of-sample predictions. This study makes two contributions to the literature on nuclear proliferation and the larger policy debate. First, it identifies for the first time an empirically grounded set of nuclear "triggers"— conditions under which countries are most likely to shift from latent nuclear capacity to a full-fledged nuclear weapons effort. Understanding these triggers has become increasingly important, as more states have begun to pursue a nuclear hedging strategy in which they seek dual-use nuclear capabilities without committing to a weapons program. Second, this study helps to reconcile conflicting empirical findings in the literature. Predictive analytics provide a new and useful way of understanding the substantive significance of existing empirical findings, and of comparing the relative importance of different theoretical approaches. ; Project on Advanced Systems and Concepts for Countering Weapons of Mass Destruction (PASCC) at the Naval Postgraduate School, Award #N00244-15-1-0003

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 data set 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.

A substantial literature examines the causes of nuclear proliferation, but few studies have addressed why states decide on a particular portfolio of weapon 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 data set of nuclear weapon 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. [Reprinted by permission of Sage Publications Inc., copyright holder.]

A substantial literature examines the causes of nuclear proliferation, but few studies have addressed why states decide on a particular portfolio of weapon 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 data set of nuclear weapon 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.