This paper provides empirical evidence in support of the clash-of-civilizations view on the nature of interstate conflicts in the post-Cold War era. First, we show that countries belonging to different civilizations have a higher probability of interstate conflict before and after the Cold War period, but not during the Cold War. Second, we explain the differential impact of civilizations on conflict over time by providing evidence that civilizational differences were suppressed during the Cold War by ideology and super-power camps. Third, we provide evidence that the component of civilizations that matters the most for conflict in the post-Cold War period is language, and not religion. Fourth, we analyze the long-term cultural, geographical and historical determinants of civilizational differences, and show that language has the largest explanatory power.