This dataset provides force structure estimates for the nine de jure and de facto nuclear states through the year 2000. Our dataset includes deployed nuclear platforms for the United States

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Do “nuclear umbrellas” create a moral hazard that can increase the risk of war? In this article, we investigate whether situations of extended deterrence in which a nuclear patron makes a defensive commitment to a nonnuclear client state can inadvertently increase the likelihood that a client will initiate a crisis with another state. Using data on the crisis behavior of states from 1950 to 2000, we estimate the impact of a nuclear umbrella on various crisis outcomes, including the initiation and escalation of militarized conflict. Interestingly, we find no evidence that such commitments increase the risk of war or even two-sided violence at lower levels. However, consistent with both the moral hazard logic and bargaining theories of war, we show that this appears to be because potential target states offer increased policy concessions to client states to avoid costly fighting. Thus, the link between nuclear umbrellas and moral hazard appears to be real, but it is reflected in the division of benefits rather than a greater likelihood of war. The results have important policy implications as the US contemplates extending its nuclear umbrella.

This chapter presents the core theoretical framework in this study: an analysis of nuclear reversal at the systemic level and the conditions under which the international community is able to induce a proliferator to abandon a nascent nuclear program. Specifically, it introduces a novel theoretical approach that highlights the necessity to negotiate with both positive and negative inducements in the shadow of military force. In addition to including the core hypotheses for empirical testing, it includes a discussion of probabilistic conditions to help examine a broader set of proliferation cases. These conditions include the impact of leadership change on the association between inducements and nuclear reversal, as well as how a proliferator’s relationship with the United States influences the likelihood of nuclear reversal. It concludes with potential limitations and overarching policy implications of the framework.

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