Alliances, internal information, and military conflict among member-states

We offer a theory explaining how alliances as international security regimes reduce military conflict between member-states through their internal provision of information concerning national military capabilities. Bargaining models of war have shown that a lack of information about relative military capabilities functions as an important cause of war. We argue that alliances provide such information to internal participants, and greater knowledge within the alliance about member-state military capabilities reduces certain informational problems that could potentially lead to war. This internal information effect, however, is a conditional one. We posit that the information provided within the alliance matters most for dyads at or near power parity: the cases where states are most uncertain about who would prevail if a military conflict did emerge. In power preponderant dyads where the outcome of a potential military conflict is relatively certain, the internal information provided by military alliances becomes less important. Our statistical results provide strong support for these theoretical arguments.