A necessary condition for the emergence of civilization (in its broadest sense, as in the collectively organized reshaping of one's living environment for one's purposes) is a basic level of trust and cooperation.

Humans are not naturally prone to bouts of violence like other species and human societies do not tolerate impulsive violence in adults. Instead, the vast majority of human-on-human violence is deliberate: people plan, carefully and rationally, the killing of their fellow human beings in order to achieve their goals. This is known as 'war'. This is very rare among species, and more violent species cannot form complex societies at scale, despite being also quite smart in some cases (chimps, octopuses).

We even unconsciously internalized this idea to some degree, since most people are comfortable with the idea of militaries existing and being necessary but also agree that solitary murderous psychopaths should be put in prison.