UC San Diego

How do “middle” states respond to intensifying great power rivalry, and what role do security institutions play in the strategies of middle states? In answering these questions, I address two gaps in the literature. First, traditional theories of alignment—balancing, bandwagoning, and hedging—each focus on a middle state’s relations with the competing great powers. Yet they fail to address how middle states interact among themselves. The second gap concerns the role of security institutions in the strategies of middle states. Balancing and bandwagoning emphasize the role alliances play as states respond to shifting distributions of power. Yet since the end of the Cold War, alliances have remained relatively stagnant and few new alliances have been formed. New “anarchic” forms of security institutions have emerged, including defense cooperation agreements (DCA), institutionalized defense dialogues, and reoccurring combined military exercises. However, these forms of security institutions currently find no part in existing theories of alignment. I introduce a theory of diversification to describe how middle states respond to shifting distributions of power and intensifying great power rivalry. Rather than just align with one of the competing great powers through bandwagoning or balancing, or engage with both by hedging, middle states also seek to diversify by strengthening security ties among themselves. Using an updated dataset of all DCAs between middle states in the Indo-Pacific, and novel datasets of all institutionalized defense dialogues and combined military exercises in the region, I show the central role these security institutions play in the strategies of middle states as they respond to growing Chinese power and intensifying U.S.-China rivalry. Using statistical, network, and detailed case study approaches, I show that middle states who face a significant threat from the rising power, have a weak commitment to alliance, are militarily capable, or who are economically developed, are more likely to employ a diversification strategy. I also show that as middle states seek to diversify, they are more likely to form a security partnership with middle states who have similar foreign policy preferences, are close economic partners, share a common security partner, or who face a common adversary.