> And we honor our veterans, and for a good reason. (Without them, we would be captured/killed by other veterans, and honor them anyway). Modern civilizational culture is a thin patina on top of our primal behavior.

This is too cynical a take. "Tribal" warfare (what, Africa, North America?) seems to not be anything compared to civilizational war machines. Evidence shows it instead is two groups shooting arrows at eachother or engaging in non-bladed physical combat - think the PRC vs India in the mountains - with maybe one death. Sort of a mutually accepted way to "blow off steam."

Given that these kinds of battles exist throughout history, alongside catastrophic civilizational ethnocides, we can't assume one or the other is our "core primal behavior." Seems we have a tendency to both, depending on circumstance.

What is universally true though, preceding our capability to organize into warbands, is the fact that our evolutionary advantage is derived from our social nature. We rule the planet because we're so social we're the only species that invented language so as to communicate very complex topics. So in terms of "natural order" for humans, and adaptive behavior, it clearly is cooperation.