The Effects of Political Similarity on the Onset of Militarized Disputes,1816-1985

Historical evidence suggests that international conflicts often concern the management of domestic affairs. States frequently take issue with other states' human rights records and with the composition of their goernments. If domestic politics are frequently the issue in dispute between states, then we should not expect such disagreements to be equally likely to arise between all pairs of states. Since politically similar states manage their domestic affairs in similar fashion, they are less likely to disagree over domestic politics and thus less likely to be involved in conflict. To test the hypothesis that politically similar states are less likely to engage in conflict than are politically disparate states, I use a hazard model that evaluates the risk that peace ends with the onset of a militarized dispute for all dyads in the international system from 1816 to 1985. I find strong support for the hypothesis, even when I control for the pacifying effects of similar democratic states and exclude data from the ideologically charged 20th century. I also find consistent evidence that conflict becomes more likely as the power of each state in the dyad increases, as the geographic distance between states declines, and as the number of past disputes increases. I find weaker support for the pacifying effects of alliances and the dangers of power parity.