Democracies are thought to behave differently than other states when cooperating in alliances, organizations, trade, and a host of other international institutions. We contend, however, that these democratic differences largely depend upon geopolitical environments that make cooperation possible. Though studies have demonstrated endogeneity between democracy and peace, few analyze the effects of this joint relationship on democratic differences in cooperative foreign policy behavior. We address this using the alliance literature as an example. We argue that alliances are used to either deter aggression or serve as conduits to advance other goals. Alliances that deter occur in dangerous environments, while those that serve other purposes cluster in peaceful environments. We find that alliances used to deter are particularly unreliable scraps of paper, and that the general reliability of alliances is concentrated among those existing in already-peaceful environments, which are unlikely to be invoked. By jointly modeling regime type and political environment using data on alliance termination from 1920 - 2001, we show that alliance reliability is a function of the latter rather than the former. Our argument has important ramifications for a host of literatures focused on regime type, as well as current debates over the effectiveness of democratic deterrence.