The indefinite extension of the Nuclear Non-Proliferation Treaty (NPT) at the 1995 Review Conference represents a pivotal moment in the history of one of the most successful and consequential arms control agreements ever made. How did it happen? Michal Onderco’s fascinating book offers an empirically rich account of the extension decision.

The primary contribution of Onderco’s book is the wealth of novel empirical detail it offers on this crucial historical episode. This alone makes the book worthy of the attention of scholars of the NPT and nuclear nonproliferation more broadly; the book will come to be the definitive account of the 1995 Review Conference for political scientists seeking to use this case in their own research. Drawing from an impressive array of interviews, oral histories, memoirs, and archival documents, Onderco’s book offers a detailed and vivid account of the key moments in the negotiation of the extension decision.

Even though indefinite extension was supported by the United States, it appeared unlikely to most observers at the time that it would succeed in persuading a majority of states to support its position. Onderco’s empirics thus focus particularly on US efforts to persuade the EU, South Africa, and Egypt to support (or at least not oppose) an indefinite extension. Each chapter offers a wealth of empirical detail on the diplomatic back-and-forth leading up to the Review Conference. The chapter on South Africa is particularly impressive. Using a range of sources including many declassified archival documents, Onderco sheds light on both the internal bureaucratic and interpersonal dynamics within the South African government, as well as the high-level interactions between US and South African leaders that ultimately resulted in South Africa supporting indefinite extension. Onderco also persuasively shows how crucial South Africa’s role was in achieving the ultimate outcome of indefinite extension by ensuring that the nonaligned movement would not offer a united front against indefinite extension.

To explain the extension decision, Onderco offers a theoretical argument that draws on network theory. He argues that it was the centrality of the United States within a range of distinct international networks that allowed it to persuade other key countries, which in turn were important nodes within their own networks. For example, the United States was able to persuade South Africa to support indefinite extension, which then exploited its own influence within the non-aligned movement. And the United States persuaded the EU to back its position; in turn the EU was able to use its influence among the postcommunist countries of Eastern Europe and Central Asia that aspired to build closer relationships with it. It is therefore the “networked power” of the United States, Onderco argues, that was crucial to explain its success in securing the support needed for indefinite extension.

No book is perfect, and Onderco’s argument does leave some open questions. For example, he presents the theoretical argument as distinct from existing realist accounts focusing on material power, institutional accounts emphasizing the functional utility of the NPT, or constructivist explanations emphasizing the fairness of the ultimate deal to extend the treaty (pp. 7–9). But Onderco’s theory does not always seem wholly theoretically distinct from those arguments and indeed incorporates many of their insights. After all, it is the material power of the United States that to a significant degree explains the position it occupies within international networks and the resources it has to offer other states in exchange for adopting positions it supports. It is the functional utility and success of the NPT in constraining the spread of nuclear weapons that explain why there was widespread support for preventing the collapse of the treaty. And it was the substantive concessions that the United States offered to assuage the concerns of other countries (particularly Egypt) that explains why it was ultimately able to make the most of its strong network position and persuade other countries to support its position. In short, Onderco’s theory seems in many ways to synthesize existing theoretical accounts of the NPT’s extension rather than offer an entirely new theoretical approach.

Similarly, the empirical evidence Onderco offers sometimes seems to support a range of theoretical interpretations: the evidence is certainly consistent with Onderco’s theoretical argument but also seems consistent with potential alternative explanations. To take one example, South African vice president Thabo Mbeki’s decision, after a series of meetings and exchanges with US vice president Al Gore, to support indefinite extension in the expectation of “a future benefit for his country from the relationship with the U.S.” (p. 81) seems equally consistent with a crude theory based on realpolitik and quid-pro-quo deal making as it does with Onderco’s network-based theory. Further, because the book focuses primarily on US negotiations with South Africa, Egypt, and the EU, it would be interesting for future research to examine whether those countries’ influence spread in their own networks in the way that Onderco’s theoretical argument would anticipate. Indeed, this would arguably offer a more challenging test of Onderco’s argument because these states lacked the raw material power of the United States that might be a confounding variable in assessing the effect of its network position. For example, the book offers limited evidence of the mechanisms through which South Africa influenced other members of the nonaligned movement. This would be a fascinating subject for future researchers to tackle.

A final question relates to other plausible outcomes from the Review Conference. Although Onderco convincingly shows that many analysts and participants did not anticipate indefinite extension prior to the conference, it remains unclear whether any other outcome truly offered a viable alternative that a coalition could have cohered around. Indeed, as Onderco shows (pp. 26–30), the other key alternatives all suffered from critical flaws, including a lack of support from states or incompatibility with the legal structure of the NPT. And there was widespread support for preventing the NPT from collapsing, which meant agreement on some form of extension may always have been the most plausible outcome. If so, perhaps the indefinite extension of the NPT is less of a puzzle than it might initially seem and was in fact always a more likely outcome than those at the time realized.

These questions do not diminish the significance of Onderco’s contribution and the light he sheds on the history of the NPT’s indefinite extension. His book deserves to be widely read by scholars of nuclear proliferation and should become the definitive account of a crucial episode in the history of international arms control.