This chapter identifies the track record of the regime – its recent history of compliance – as a key driver of the decisions of states to abide by their nonproliferation commitments. The argument begins with the simple idea that the regime is based on a fundamental bargain among member states: each member is willing to comply only so long as others do. When states join the regime, they do so with some expectation about its performance—the extent to which other states ultimately will abide by their commitments. There is often significant uncertainty surrounding this expectation, however, and new information about the performance of the regime will help resolve uncertainty and influence compliance. The track record of the regime provides the best source of such information. As time passes with few violations, states will in turn be more likely to comply themselves. Evidence of rampant noncompliance, on the other hand, will make states more likely to cheat. This logic is reflected in Japan’s consideration of nuclear weapons development over the years and is supported by statistical tests using data on nuclear weapons programs by NPT members.

Scholars often point to pressure from the United States as a key factor in driving membership in the nuclear nonproliferation regime, but this explanation has trouble explaining the changes we see in patterns of membership over time. This chapter shows that variation in the perceived effectiveness of the regime – as indicated by overall membership, the strength of verification measures, the effectiveness of enforcement, and a history of cooperation – better explains why states join. Member states are reluctant to forgo nuclear weapons without assurances that others will comply as well, and signals of regime effectiveness reassure states that their commitments will be reciprocated. This argument runs counter to the conventional wisdom among international organizations scholars, that there is a “depth versus breadth” tradeoff in institutional design. Drawing from archival documents, this chapter discusses the illustrative cases of the NPT ratification decision in Australia and Switzerland. It then tests its theory using data on state membership in the NPT.

The NPT was met with skepticism when the treaty first went into force, and 50 years later analysts are still predicting its imminent demise. This chapter highlights the central puzzle of the book: why does the nuclear nonproliferation regime – which most expected to have limited effectiveness – appear to have been so successful? Tracing the history of the regime, it draws from declassified documents and diplomatic records to examine how events have shaped perceptions of the regime’s effectiveness. It describes the parallel expectations of international organizations and international security theory and contrasts the widespread pessimism about the regime with evidence of its success.

The nuclear nonproliferation regime lacks formal enforcement mechanisms, but this does not mean that violations of nonproliferation commitments always go unpunished. States that violate the NPT routinely face pressure from others to change their behavior, including through economic sanctions. But the lack of formal enforcement measures does contribute to significant variation in the states that are targeted for punishment – enforcement is always at the discretion of the punishing state. Why do some states face punishment while the transgressions of others are overlooked? This chapter argues that enforcing states look to the policy preferences of violators for signals about the likelihood that enforcement will change state behavior and about the cost to the international community of allowing the violation to continue. Patterns of institutional membership within the larger regime help to credibly reveal the preferences of state parties. Using data on membership in the various agreements that make up the nuclear nonproliferation regime, this chapter shows that violating states are less likely to face costly enforcement action the more embedded they are within the regime.

A core promise of the nuclear nonproliferation regime is that it will provide nonnuclear weapons states with access to civilian nuclear technology. At the same time, nonproliferation advocates see the regime as a major tool in limiting the development of this dual-use technology and the spread of nuclear weapons. This chapter examines the effect of membership in the nonproliferation regime on the provision of nuclear latency – the underlying capability to quickly acquire a nuclear weapon. Using data and findings from the previous chapters, it shows that regime membership, for all its positive effects, comes at the cost of contributing to members’ latent nuclear capability.

The final chapter of the book summarizes its central argument and expands on the policy implications of the study. The preceding chapters, for example, suggest that perceived weaknesses in the nuclear nonproliferation regime could act as a proliferation trigger, pushing states to take that final step toward nuclear pursuit. This raises the stakes for policymakers in maintaining the credibility of the regime, by reassuring allies, committing to punishment of violators, and closing persistent regime loopholes. At the same time, the link between regime membership and latent nuclear capability suggests that confidence in the constraining power of the nonproliferation regime could give us a false sense of security.

The opening chapter gives a general outline of the nuclear nonproliferation regime, summarizes the argument and approach to the subject, explains the book’s contribution to the literature and policy debate, and provides an overview of the remaining chapters.