Recent events around the world have convinced political scientists and policymakers that nationalist conflicts are an important feature of the post-Cold War world. Conflicts in Bosnia, Chechnya, Kosovo, and Kurdistan have all been prominent in headlines in recent years; but such conflicts are not just a post-Cold War phenomenon, and many have been going on for decades. This article outlines the scope of this phenomenon - violent conflicts between nationalist groups within states - in the post-war period. It presents a dataset of violent nationalist conflicts within states from 1945 to 1996, measuring cases in terms of initiation, duration, and intensity of conflict, and comparing this effort to other intrastate conflict data collections. The characteristics of these conflicts before and after the Cold War are examined, to test the popular notion that the end of the Cold War has `unleashed' a new era of nationalist strife. This survey concludes that these conflicts are not simply a post-Cold War phenomenon, nor has the end of the Cold War brought an unprecedented wave of new nationalist conflicts to the world. On the contrary, many such conflicts do get resolved, and more have been resolved in the past ten years - particularly by peaceful methods - than in any comparable period in recent history.