Traditional interpretations of politics among nuclear-weapons states—as epitomized by Schelling’s theory of deterrence through mutually-assured destruction—are less useful in today’s proliferation environment than they were during the Cold War’s superpower rivalry. As regionally-important states begin to pursue nuclear weapons, they do so in an environment that is shaped by the preferences and behaviors of the great powers. Using an elaboration on Powell’s bargaining model of conflict, this article shows that nuclear proliferation radically alters the future distribution of power, introducing a commitment problem vis-à-vis conventionally-stronger neighbors. This explains the occurrence of preemptive war in cases of attempted nuclearization, although the empirical paucity of such bargaining failures requires the shadow of great-power intervention in understanding the relations of second-tier states.