Our Species has a long history of distrusting strangers, despising outgroups, and fighting each other in many ways and many places, using the most damaging technology available at the time. This special issue of Science on Human Conflict illustrates the role of the scientific community in achieving deep insights into the evolutionary history of human conflict and, most importantly, demonstrates how science can help to clarify the major factors that affect the risk of mass violence (see p. 818). Such understandings are critical to develop education that decreases the probability of conflicts, to provide early and active help to countries having trouble with intergroup relations, to help foster equitable democratic development, to protect and promote human rights, and to place constraints on weaponry.