What strategies do states follow in developing nuclear weapons? Most research on the politics of nuclear weapons focuses on which states decide to seek the bomb and whether they get it. Vipin Narang’s new book instead offers a comprehensive analysis of how states seek the bomb. It provides a clear categorization of the strategies available to states, develops a theory of why states choose a particular strategy, and presents a mountain of qualitative evidence to support this theory. One could quarrel with elements of the categorization and theory, and especially with the interpretations of some of the cases. However, overall this book is a careful and thorough treatment of an important aspect of the politics of nuclear weapons that should be read by all scholars of the field.

Cleverly, Narang’s categorization of how states seek the bomb ignores the technological aspects—such as choosing either uranium or plutonium as the key component of a bomb—that are the focus of much expert commentary on nuclear weapons programs. Instead, the book zeroes in on variation in the political objective a state wishes to achieve with its program. States that wish to obtain the capability to build the bomb, but not the bomb—called “hedgers”—are thus different from those that want nuclear weapons. Both categories are further divided into three varieties. “Technical” hedgers see no immediate reason to have nuclear weapons but wish to be ready should one arise well into the future. “Insurance” hedgers rely on the protection of a powerful ally but worry that this might lapse in the near future. “Hard” hedgers feel nuclear weapons are needed but intentionally stop just short of assembling them. Among active pursuers of the bomb, “sprinters” do so openly and quickly; “sheltered pursuers” do so under the protection of a sympathetic major power; and “hiders” try to get the bomb stealthily rather than speedily.

This categorization discretizes choices that are probably more continuous in reality. Active pursuers vary in the balance they choose between getting the bomb quickly or instead quietly: The Soviet Union is classified as a sprinter, but it was careful to hide the progress and facilities of its program from the United States. The hedgers also seem to vary only in degree, with the result that the differences among them are not always clear. Still, Narang’s categorization represents an important advance over previous work that either oversimplified states’ strategies—as “exploring” or “pursuing” nuclear weapons, in the most widely-used empirical measure—or submerged them in a sea of technical details.

Narang theorizes that states’ choices of strategy are driven by certain characteristics of their political environment. If it faces no acute, severe military threat, a state elects for technical hedging. In the presence of such a threat, it chooses insurance hedging if, for the foreseeable future, it can rely on a security patron for protection, and otherwise chooses hard hedging if it has no protection but cannot yet generate the domestic political consensus needed to go nuclear. If this consensus is present, it actively pursues the bomb, openly sprinting if it does not fear military or economic prevention, under shelter if it enjoys temporary protection from a major power, or in hiding if it does not.

This theory of why states choose a particular strategy for seeking the bomb is a major contribution. Previous theoretical work on proliferation mostly treats it as all or nothing: States either pursue the bomb or do not. One partial exception is my own research with Muhammet Bas, which theorizes that states might develop an advanced nuclear program as leverage with outside states, rather than to build weapons, paralleling Narang’s delineation of hedging from active pursuit (see, most recently, “Give Peace a (Second) Chance: A Theory of Nonproliferation Deals,” International Studies Quarterly, 2018). This book goes further, however, in identifying variation within hedging and active pursuit and showing how this variation is driven by factors like the speed versus stealth trade-off.

The theory considers only the effect of the state’s political environment on its choice of proliferation strategy. Of course, a state’s choice can also affect its political environment. A nuclear weapons program, if detected, can create an acute threat where none previously existed, or lead a security patron to rescind its protection, and the international reaction can undermine domestic political consensus for the bomb. Neglecting this strategic interaction sometimes leads to odd interpretations of cases, as when the book argues that Iran switched from hiding to hard hedging because its domestic political consensus for the bomb fractured. A more straightforward explanation would be that Iran switched because it got caught, and had to make a deal with the United States to avoid continued sanctions and a possible attack.

Across 29 countries that sought the bomb, the book identifies and codes 46 choices of strategy, and finds that the theory is confirmed in 40 of those choices, or about 85 percent. The bulk of the book is given over to 16 case studies of particular states’ choices of proliferation strategy. Declassified documents, interviews with relevant policy makers, and prior case histories are used to code each state’s strategy and demonstrate that the theory’s proposed mechanisms played a role in determining that strategy. The book’s treatment of each case is thorough and provides an excellent synthesis of the available primary and secondary sources.

The coding of some of these cases, and the corresponding interpretation of the evidence, however, is not always convincing. Israel is plausibly coded as a sheltered pursuer, but with France rather than the United States as its protector. China is coded as sprinting and South Africa as hiding, even though each was arguably sheltered by a superpower that acted to stop the other superpower from attacking their programs. Perhaps most controversially, North Korea is coded as being sheltered by China, despite the fact that China did not stop the United States from threatening comprehensive sanctions and preparing to launch an attack on North Korea’s program in the early 1990s. Still, even if one were to hold these and other ambiguous cases against the theory, it would be supported more than 60 percent of the time.

None of these concerns should distract from the very substantial step forward that this book represents. Its novel categorization of proliferation strategies, clear theory for states’ choices of strategy, and careful dissection of the empirical evidence on these choices all distinguish it as one of the most important works on the politics of nuclear weapons. Indeed, an initiate to this field could do much worse than to begin by reading this book in conjunction with Narang’s previous book, about the strategies states choose for their nuclear weapons once they have acquired them (Nuclear Strategy in the Modern Era: Regional Powers and International Conflict, 2014).