There was hope after World War II that the horrors of the Holocaust, Nazi Germany's crusade against Jews, and the killing of millions of other people would bring such violence to an end forever. Instead, collective or group violence has become commonplace in the second part of the twentieth century. Cambodia, China, Indonesia, Tibet, East Timor, Argentina, El Salvador, Chile, Guatemala, Colombia, Bosnia, and Rwanda are only some of the better-known places where such violence has been perpetrated. Its forms have also been numerous, including genocide, mass killing, abductions or disappearances of large numbers of individuals, and widespread torture (Suedfeld, 1990).

Without effective prevention, the frequency of such violence is likely to rise further in the twenty-first century. Poverty, the experience of injustice, and social and psychological disorganization that prevents the meeting of basic human needs in a rapidly changing world tend to lead people to turn to ethnic, religious, national, or other “identity” groups to strengthen individual identity and to gain support and security. This, combined with ideologies that groups adopt in difficult times, whether Nazism, communism, nationalism, racial supremacy, or something else, frequently leads to antagonism and violence against other groups.

Understanding the influences that lead to collective violence is necessary for prediction; both understanding and prediction are essential for prevention. For effective prevention, it is highly important to further our understanding of commonalities in both causes and methods of prevention as well as to respect the particulars of each potentially violence-producing situation.