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.国际军备控制条约如何影响国家政策？本文以《不扩散核武器条约》（Nuclear Nonproliferation Treaty, NPT）的效力为分析对象，对这一问题展开研究。尽管近数十年来学界对此展开了激烈争论，但学者们仍未能全面厘清该条约是否真正“发挥效用”。这场争论持续存在的部分原因在于，既有研究存在一项核心局限：其设计初衷并非用于推断NPT成员国身份与核扩散之间的因果关联。此前的研究无法判定，究竟是条约成员国身份约束了国家研发核武器的行为，还是仅反映了国家既有的核政策偏好。为弥补这一局限，本文通过测算国家事前的条约承诺偏好，来控制选择效应偏差。通过对1970年至2000年的核扩散情况展开分析，本文的研究结果表明，NPT在遏制核武器扩散方面发挥了关键作用。即便在考虑了国家出于战略考量选择加入条约的情况后，NPT批准仍与国家研发核武器的可能性显著负相关，且这一关联具有稳健性。本文的研究结论不仅为《不扩散核武器条约》与核不扩散领域的学术争论提供了新的洞见，也为探究国际制度如何影响国际政治的相关研究提供了广泛的启示。