The Determinants of Nuclear Force Structure

A substantial literature examines the causes of nuclear proliferation, but few studies have addressed why states decide on a particular portfolio of weapon systems once they have acquired a basic nuclear capability. We advance a portfolio theory of nuclear force structure, positing that states seek a diverse set of capabilities for nuclear deterrence, but that they also face major resource and organizational constraints. A number of factors may help to explain the portfolio of nuclear forces that states ultimately field, including resource availability, experience as a nuclear power, bureaucratic politics, the conventional threat environment, the presence of nuclear rivals, and the maintenance of nuclear alliances. We test the influence of these factors on force structure using a new data set of nuclear weapon platforms fielded by nine nuclear nations between 1950 and 2000. Our findings represent an important step in understanding the drivers of nuclear behavior after states have joined the nuclear weapons club.