Research on military alliances generally pays little heed to changes in the obligations and characteristics of military alliances that states negotiate and form over time. This lack of attention to systematic changes in the structure and content of alliance treaties is a puzzle, especially when one considers how international relations scholars link different domestic political structures to variation in foreign policy behavior. In this paper, we build upon theory from the democratic peace and military alliance research programs to consider the implications of democratic governance on the nature of military alliances. Treaty obligations commit members to act in future international crises or military conflicts and therefore the risk that leaders will involve the nation in costly foreign conflicts increases. Democratic systems of government produce incentives for leaders to be cautious when conducting foreign affairs because of the ease by which constituents can punish leaders’ foreign policy failures with removal from office. Consequently, differences in domestic regimes create incentives for leaders to design and form different types of alliance treaties. Because the last two centuries contain a remarkable amount of change in domestic political institutions throughout the international system, we argue that the emergence of more democratic regimes will influence the types of military alliance commitments formed by states.