A winning proposition? States’ military effectiveness and the reliability of their allies

This article explores the relationship between states’ past military performance in interstate wars and the likelihood that their allies will come to their aid when the terms of their alliance require intervention. Following Leeds, I argue that decisions to honor or violate alliances depend on changes that have occurred since the signing of the alliance and various factors that affect the expected costs of honoring the alliance. What I add to this approach is an exploration of whether and how a state’s performance in prior interstate wars sends signals about its likely military effectiveness in the current war. I argue that superior records of military performance signal to allies that their potential costs for intervention will be lower than they would be with a less effective ally. I use an outcomes-based measure of military effectiveness to predict when states will violate or honor their alliances.