Strategies of Extended Deterrence: How States Provide the Security Umbrella

Abstract

What extended deterrence strategies are available to nuclear patrons, and what factors determine which strategy they adopt? How does each strategy manifest as force employment? The bulk of the literature on extended deterrence focuses on its effectiveness. The question of how nuclear patrons select between and employ strategies of extended deterrence, however, has largely been overlooked. Addressing the first, or strategy adoption, question, I argue that the interaction of two variables—(1) the type of threat posed to a client by an enemy; and (2) the likelihood of an enemy’s quick victory over a client—determines a nuclear patron’s strategy among four options: a conventional defense pact, forward conventional deployment, a nuclear defense pact, and forward nuclear deployment. Addressing the second, or strategy implementation, question, I argue that each strategy is embodied as the unique mixture of conventional and nuclear forces pre-positioned in either forward or rear areas. I test my theory of extended deterrence in two ways. First, I conduct a congruence test. Second, I perform two case studies—US extended deterrence to South Korea and the Philippines. I conclude with a discussion of policy implications for the current US security commitments to Seoul and Manila.