The Effect of Age Structure on the Abrogation of Military Alliances

Scholars of alliance politics have ignored a potentially important factor that shapes foreign policy: the age structure of a state. In this article, we argue that an alliance member is more likely to terminate the alliance in violation of the terms when the state’s youth ratio is high. The demographic pressure of a high youth ratio raises potential for political instability domestically, which in turn increases the risk of radical foreign policy changes. We demonstrate the effects of a state’s age structure on its alliance policy by examining alliance termination by violation from 1950 to 2000. Through quantitative analysis, we find that youth ratio is a strong and significant predictor of alliance abrogation. A brief examination of several examples illustrates two paths by which the pressure created by a high youth ratio contributes to political instability and results in alliance abrogation—leadership change that brings about a new foreign policy and appeasement of the population through abrogation of an unpopular alliance.