Huntington's (1993a, 1993b, 1996) clash of civilizations thesis suggests that states belonging to different civilizations are more likely to become involved in conflict with one another. To evaluate the empirical accuracy of Huntington's claims, we examined the relationship between civilization membership and interstate war between 1816 and 1992. We find that civilization membership was not significantly associated with the onset of interstate war during the Cold War era (1946–1988), which is consistent with one aspect of Huntington's thesis; however, we also find that for the pre–Cold War period (1816–1945) states of similar civilizations were more likely to fight each other than were those of different civilizations, which contradicts Huntington's thesis. Most importantly, our analysis reveals that during the post–Cold War era (1989–1992), the period in which Huntington contends that the clash of civilizations should be most apparent, civilization membership was not significantly associated with the probability of interstate war. All told, our findings challenge Huntington's claims and seriously undermine the policy recommendations that devolve from his clash of civilizations thesis.