| Summary/Abstract |
We develop a formal model of bargaining between two states where one can invest in a program to develop nuclear weapons and the other imperfectly observes its efforts and progress over time. In the absence of a nonproliferation deal, the observing state watches the former's program, waiting until proliferation seems imminent to attack. Chance elements—when the program will make progress and when the other state will discover this—determine outcomes. Surprise proliferation, crises over the suspected progress of a nuclear program, and possibly “mistaken” preventive wars arise endogenously from these chance elements. Consistent with the model's predictions and contrary to previous studies, the empirical evidence shows that the progress of a nuclear program and intelligence estimates of it explain the character and outcomes of most interactions between a proliferant and a potential preventive attacker. Counterintuitively, policies intended to reduce proliferation by delaying nuclear programs or improving monitoring capabilities may instead encourage it.
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