Scholars increasingly are accepting the empirical generalization that democracies almost never go to war with each other, and infrequently even engage in militarized disputes with each other. It has not been clear, however, whether the rarity of conflict between democracies is caused by some aspect of being democratic, or whether it is caused by some other variable or variables that may be correlated with democracy. Using data on all independent states for the period 1946-1986, we examine the effects of political system type, distance, wealth, economic growth, alliances, and political stability. The results suggest that, although most of the other variables do have an effect, as hypothesized, there still seems to be an independent effect of political system type: democracies engage in militarized disputes with each other less than would be expected by chance. The effect may be enhanced by political stability; that is, states which can be perceived as stable democracies are less likely to be involved in disputes with other democracies.