Macro-coalitions within groups facilitated sociopolitical integration across groups. Thus, societies grew. Such an evolutionary transition was made possible through multilevel selective pressures promoting cooperation between these local political entities against supralocal political entities. In other words, operating under the assumption that my enemy’s enemy is my friend, adjacent groups allied with one another against more distant outgroups, and, over time, merged into larger groups. It is important to understand the evolutionary transition to larger groups, because only in larger groups can sociopolitical complexity arise. Yet, as we also detail herein, with the growth of group size, came intensified violence and despotism. Several publications have reported such a curvilinear trend wherein warfare frequency and proportional killings increase from bands to tribes and eventually reach a zenith with simple and complex chiefdoms; thereafter, warfare frequency declines as complexity increases further among inchoate, ancient, modern, and contemporary states. In addition to reviewing those many publications studying interactions between warfare frequency, sociopolitical complexity, and lethal aggression, this chapter analyzes archaeological and ethnographic literature on lethal aggression in small-scale societies, providing empirical evidence concerning effects of direct and indirect influences of human-animal symbiotic associations, culture of honor, and external warfare between two distinct biocultural groups on sociopolitical complexity. Precedents for such interactions are comparatively rare. The rationale for including this seventh chapter is the same as the rationale for including the sixth: A more convincing ultimate explanation of modern political psychology comes from understanding the origins of brain and behavior as they are evolutionarily and culturally bequeathed from nonhuman primates and small-scale societies. It was through these transitions that selective pressures instilled genetic differences in the insula, amygdala, and other brain regions that give rise to those temperamental, perceptual and emotional differences undergirding political orientation.