Are humans naturally violent? If so, how do we explain the large differences in violence rates across cultures and nations? Why is the United States among the most violent of industrialized countries? Why are most of us non-violent and a few of us excessively so? Psychologists and other social scientists have studied violence for many decades, but modern approaches draw heavily not only on traditional psychological, sociological and cultural theories, but also on evolutionary psychology, genetics, and neuroscience. Although many people seem to think that we need a special, esoteric, psychology to explain the behavior of violent people, almost all forms of violence can be explained using fairly straightforward psychological principles supplemented by knowledge of biological, societal and cultural factors.