Alliances and Asymmetry: An Alternative to the Capability Aggregation Model of Alliances

This paper proposes an alternative logic of alliances to the capability aggregation model where both allies receive security from an alliance. In this alternative logic, one partner receives autonomy benefits, and the other, security benefits from the alliance. The former type of alliances are called symmetric and the latter asymmetric. The paper develops both logics from a model of alliance choices in the face of trade-offs between autonomy and security and provides a precise definition of those two concepts. It then derives a series of critical tests that show the trade-off model is superior to the capability aggregation model. First, asymmetric alliances will be easier to form and last longer than symmetric alliances. Second, regardless of the type of alliance, the greater the change in its members' individual capabilities, the more likely it will be broken. Third, second-rank major powers will be more likely to form asymmetric alliances as their capabilities increase. All the hypotheses are supported by a statistical examination of military alliances formed between 1815 and 1965. The implications of the argument for several topics in international relations theory are drawn out.