Scholarship on nuclear security has extensively explored the causes of nuclear proliferation, and the question of why states pursue or refrain from nuclear weapons programs. It has neglected a logical follow-on question—once a state builds nuclear weapons, what nuclear strategies does it pursue? Nuclear Strategy in the Modern Era makes a seminal contribution to the literature by examining this question, and by also tackling a related question—does the relevant nuclear strategy deter conflict? Three strong points of the book are worth noting.

First, the book develops a “posture optimization theory” to categorize and explain three types of national nuclear postures. A catalytic posture aims at “catalyzing” third-party intervention in crises. An assured retaliation posture seeks to directly deter nuclear attack by threatening an opponent with unacceptable damage (this strategy has long been recognized by deterrence theorists, who note that it requires the development of invulnerable second-strike forces). An asymmetric escalation posture aims to deter conventional attacks through the first use of nuclear weapons against an attacker. The book also explains why states adopt each of these postures. Thus, if a state has reliable third-party patrons—principally the United States—it would adopt a catalytic posture. If it does not have such patrons, and if it faces a conventionally-superior proximate offensive threat, then it would adopt an asymmetric escalation posture. And if it does not face such a threat, but has assertive civil-military arrangements (where civilian political leaders in central capitals, rather than military officers in the field, assert control over nuclear weapons), it would opt for assured retaliation.

Second, the book tests and validates the theory by examining the main non-superpower countries that acquired nuclear weapons—Pakistan, India, China, France, Israel, and South Africa. In a chapter on each of these cases, it explains that China and India adopted postures of assured retaliation; Pakistan’s posture shifted from catalytic to asymmetric; Israel’s changed from catalytic to assured retaliation; France pursued asymmetric escalation; and South Africa had a catalytic posture.

Third, adopting a multi-method research design, the book examines its second main question—does each of the above postures deter conflict? Thus, statistical tests and a multinomial logit analysis confirm “the unique deterrent power of the asymmetric escalation posture, the persistent irrelevance of the assured retaliation postures in deterring even intense conventional conflict, and the riskiness and deterrence suboptimality of the catalytic posture” (p. 243). In other words, this analysis suggests that an asymmetric escalation posture is best at deterring conflict. This is followed by a qualitative small-n study of five India-Pakistan crises and three Arab-Israel wars. These eight examples “largely show that the asymmetric escalation posture is indeed deterrence optimal” (p. 297).

Nuclear analysts and deterrence theorists will raise two main points about this study and its conclusions. First, the three postures should be considered as ideal types—states may only partially adopt each posture, or may simultaneously pursue more than one posture. For much of the 1990s, Pakistan had a catalytic posture, and the book suggests that it shifted to an asymmetric escalation posture in 1998. Yet, during the 1999 Kargil conflict and the 2001–02 India-Pakistan crisis, Pakistan appeared to be pursuing both postures—it simultaneously sought to deter India (through the asymmetric posture) and to draw the United States into the crisis (via the catalytic posture). Indeed, even if it was pursuing just the asymmetric escalation posture (against India), the 1999 and 2001–02 conflicts eventually unfolded as if Pakistan was pursuing the catalytic posture—the United States ultimately stepped into both crises. Thus, the history of these two crises indicates that states may simultaneously adopt more than one posture; and that, even if they intend to adopt just one posture, a crisis may ultimately unfold to involve additional postures.

Second, nuclear postures must eventually be combined with conventional strategy and third-party intervention to more thoroughly explain deterrence and its shortcomings in regional conflicts. India’s behavior in the above cases is especially relevant to this point. When its nuclear assured retaliation strategy failed to deter Pakistani provocations, India adopted a conventional strategy of compellence, especially in 2001–02, and this significantly escalated the conflict. Pakistan’s asymmetric escalation posture failed to deter this Indian conventional response. In the end, however, India’s conventional compellence strategy also had a “catalytic” impact, in the sense that it drew the United States into the crisis, and Washington was instrumental in then easing the crisis. Clearly, conventional and nuclear postures are tightly linked, and they also draw third-parties into crises; by examining the interaction of these three factors (nuclear posture, conventional strategy, and third-party intervention), one can better explain how conflicts are deterred or eased.

To conclude, Nuclear Strategy in the Modern Era impressively advances scholarship on nuclear proliferation and its consequences. It does not take a firm position on the longstanding debate between deterrence optimists (who argue that nuclear deterrence keeps the peace between regional rivals) and deterrence pessimists (who argue that they do not), but it introduces a key new variable—nuclear posture—into the debate. Further research that combines this variable with other variables—conventional strategy and third-party intervention—would, perhaps, offer more nuanced answers to this enduring debate in international relations.