Do Arms Control Treaties Work? Assessing the Effectiveness of the Nuclear Nonproliferation Treaty

How do international arms control treaties influence state policies? This article investigates this question by analyzing the efficacy of the nuclear Nonproliferation Treaty (NPT). Despite fierce debate over the last several decades, scholars still lack a full understanding of whether or not the treaty “works.” This debate persists, in part, because existing studies suffer from a key limitation: they are not designed to infer a causal connection between NPT membership and nuclear proliferation. Prior research cannot determine whether membership in the treaty restrains states from developing nuclear weapons or simply reflects existing preferences. To address this limitation, this article accounts for selection effects by using a measure of states’ ex ante treaty commitment preferences. Our analysis of nuclear proliferation from 1970 to 2000 provides evidence that the NPT has played a key role in curbing the spread of nuclear weapons. Even after accounting for strategic selection into the treaty, NPT ratification is robustly associated with a lower likelihood of pursuing nuclear weapons. Our results not only matter for debates over the NPT and nonproliferation but also have broad implications for the study of how international institutions affect international politics.