The Causes of U.S. Nuclear Weapon Deployments

This paper explores the causes behind the deployment of nuclear weapons by the United States. Scholarly work on nuclear weapons has predominantly focused on strategic forces. However, many escalation scenarios foresee the use of tactical nuclear weapons as a precursor, which could eventually lead to an all-out nuclear war. These are exactly the weapons that the United States has deployed to 14 states since 1954, and we know little about their strategic causes. My study addresses this gap in the literature. I emphasize the importance of assurance, which has commonly been neglected or subsumed under non-proliferation. By providing a comprehensive conceptualization, my study distinguishes assurance from other strategies of interstate interaction and explains how the U.S. uses nuclear weapon deployments to assure allies and maintain its sphere of influence. I argue that the United States selectively deploys its nuclear weapons to allies that possess the means to act more independently from their guardian. Specifically, I test the hypotheses that nuclear deployments are determined by the maintenance of good relationships with other great powers, military power, and nuclear latency. To control for other explanations, I also examine if the deployments are more likely in highly threatened states (extended deterrence) or in strategically important geographic locations (power projection). Utilizing an original dataset, I find evidence that largely confirms my assurance hypotheses. With regard to alternative explanations, the power projection hypotheses are supported, but the extended deterrence hypotheses are not. These results contribute to the underdeveloped literature on assurance and provide valuable insights into the strategic considerations underlying U.S. nuclear weapon deployments.