The Third Leg of the Kantian Tripod for Peace: International Organizations and Militarized Disputes, 1950–85

Immanuel Kant believed that democracy, economic interdependence, and international law and organizations could establish the foundations for “perpetual peace.” Our analyses of politically relevant dyads show that each of the three elements of the Kantian peace makes a statistically significant, independent contribution to peaceful interstate relations. These benefits are evident even when the influence of other theoretically interesting factors—such as relative power, alliances, geographic contiguity, and economic growth—is held constant. Increasing the number of shared memberships in intergovernmental organizations (IGOs) by one standard deviation reduces the incidence of militarized disputes by about 23 percent from the baseline rate for a typical pair of bordering states. If both members of a dyad are democratic, conflict is 35 percent less likely than the baseline; increasing both the dyadic trade–GDP ratio and the trend in trade by a standard deviation reduces the chance of conflict by 38 percent. Together, all the Kantian variables lower the probability of a dispute by 72 percent. We check for reverse causation and find reason to believe that a feedback system is at work, with IGOs reducing conflict and low-conflict dyads joining IGOs. Democracies and interdependent states are more likely to join IGOs with one another, bringing together the three elements of a system for Kantian peace.