This article examines the extent to which cultural similarity vitiates the relationship between joint democracy and the incidence of interstate war. Previous empirical findings which suggest that cultural/normative explanations of the democratic peace are more robust than institutional/structural ones invite an analysis of the impact of broader cultural factors on the relationship between joint democracy and war involvement. The author suggests several ways that cultural factors might mitigate the democratic peace phenomenon and conducts a multivariate logistic analysis of state dyads from 1820 to 1989 to test the main query. Of the cultural variables, religious similarity within dyads is associated with a decreased likelihood of war onset, while both ethnic and linguistic similarity have the opposite effect. Democratic dyads, on average, have higher religious similarity levels than nondemocratic dyads, which, ostensibly, might play a role in reducing conflict within democratic dyads. However, the findings clearly demonstrate that although cultural factors are significant correlates of war they do not vitiate the impact of joint democracy on war. It appears that where a pair of states share a common democratic political culture it exerts a conflict dampening impact that overrides ethnic, linguistic, or religious factors.