Dominic Johnson and Bradley Thayer consider “What Out Primate Relatives Say About War” (The National Interest):
despite signs of many types of violence falling in western societies (a point recently championed by Steven Pinker), war continues unabated in the new century.
“Unabated” means no decrease. But war has abated or decreased recently.
While there are many things unique to humans, perhaps the most significant has been collective action in large groups of non-kin, and defense and offense against rival groups. Inter-group conflict may be important among chimpanzees, but Homo sapiens turned it into an art.
I would add that human males were the decisive actors in moving to large-scale non-kin cooperation. Both bonobo males and chimp males are automatically hostile to males from outside the natal group. Not so with human males. For 10,000 years until recently, it was males who created large collective action agencies such as armies, bureaucracies, companies, religious organizations and so on.
when we consider “Why war?,” we have an answer: war is one of Mother Nature’s solutions to compete successfully for resources.
For ants as well as chimps and humans. But for humans it is not just resources (including territory), but also mates, prestige, and many other of the good things people desire.
natural selection favored individuals who cooperated to avoid being killed—and, if necessary, to kill
Cooperation makes war possible, and war spurs cooperation, and traits such as desire to display courage. War made groups, and groups made war. Yet, a major question arises: why have at least some groups (like the West) become less and less in-group oriented and more encompassing?