According to this idea, the introduction of a more-effective weapon system gave social groups a safer, more-reliable way to coerce uncooperative individuals to support the efforts of the group or to seek another one somewhere else.
This, in turn, allowed social groups to grow larger without the previously inevitable splintering into rival groups based largely on family loyalties. In violent conflicts, members of larger groups would have an evolutionary advantage over members of smaller groups. As a result, larger groups requiring increased levels of social complexity would proliferate.
Story: Bradley T. Leper, Columbus Dispatch | Photo: Wikimedia Commons