Previously reported empirical evidence suggests that when conflict arises, military alliances are not reliable; state leaders should only expect their alliance partners to join them in war about 25% of the time. Yet, theoretical arguments explaining the choices of leaders to form cooperative...

The authors appraise a well-known argument connecting economics and security in international relations: military allies are likely to trade more with one another than non-allies. A review of alliance treaties and diplomatic history suggests that, under certain conditions, states may tie...