Title: Absolute Alliances
Description: What is a nuclear umbrella alliance and how does it differ from other defensive alliances in international politics? Scholars and practitioners frequently refer to this type of pact, but no study has defined it or identified how a nuclear security guarantee, as an umbrella alliance is better-termed, is unique. This dissertation presents and tests a theory of nuclear security guarantee formation and management. In Chapter 1, I establish two factors that make nuclear security guarantees novel: their ambiguous treaty content and unilateral provision of military aid. I present my Theory of Absolute Alliances, positing that these alliance attributes can be explained by the fact that security guarantees aim to establish deterrence by punishment in addition to deterrence by denial. Security guarantees' vague content and one-sided provision of capabilities, however, means that they are also riddled with vexing information problems that patron and client must manage at all stages of their alliance relations.

I derive three hypotheses on security guarantee formation, entrapment, and abandonment that are tested in this project. In Chapters 2 and 3 I present a hypothesis on nuclear security guarantee formation, positing that while the presence of shared adversaries among prospective allies may explain the formation of many defense pacts, nuclear security guarantees have more exacting conditions for formation. For security guarantees to form, prospective allies should have exclusive adversaries--that is, one or more shared adversaries and no unshared adversaries--between them. I test this proposition statistically and using case studies of the US decision to deny Israel a formal security guarantee and the formation of the Franco-Russian alliance, a non-security guarantee. In Chapter 4 I hypothesize that security guarantees' ambiguous and unilateral nature may create a heightened risk of crisis entrapment for patrons. These features serve the purposes of general deterrence, but once an ally is involved in a crisis, they also mean that the patron is inclined to intervene to clarify its commitment to a weaker ally that cannot credibly defend itself.

I test this hypothesis using summary statistics and qualitative case studies of the US-Taiwan and Sino-Soviet alliances in the 1958 Taiwan Straits Crisis. I also examine US non-intervention in the Beagle Channel Crisis, a non-security guarantee case. In Chapters 5, I present a hypothesis on client state abandonment fears. Security guarantee clients are prone to particularly acute abandonment fears, and I posit that because of the a priori information deficits in these pacts, abandonment fears can be addressed through the unilateral provision of information on patron strategies and policies. I examine case studies of NATO's Nuclear Planning Group and the Extended Deterrence Dialogues in the US-Japan alliance, and consultation in the US-Thailand alliance, a non-security guarantee. I find significant support for my three hypotheses and conclude this study with directions for future research and policy implications.