Tribal warfare was usually a matter of establishing boundaries. If I remember my history correctly, this was pretty clearly demonstrated in battles between Native Americans and European colonists in the 16 and 1700s. Tribal attacks were closer to raids - warriors would fight, some people would die, but damage on a lasting scale was minimal. Colonist attacks, on the other hand, were going to war in the civilized measure of the term; burning down villages/towns, significantly more death, etc.

And as technology has advanced and civilizations have grown in size and strength, our conception of war has grown ever more brutal. Its been shown, for example, that troops at the time of the revolutionary war that fired on each other by and large missed - troops would load gunpowder but not the bullet; they would aim over the heads of the opposing troop at the last second; and so on. Something like 20 or 30 percent of the troops would actually be shooting at their opponents.

When this was discovered (I think in the early 1900s, but I don't really remember - could be as late as the 40s?) armies changed training methods; they would use targets closer to the shape of humans and so on, and there was a massive increase in the accuracy of soldiers using guns. There was also the advent of "total war" during the American Civil War, with the previously unheard-of scale of destruction that brought (which we now consider typical).

In short, "war" is a wildly different thing for two tribes of a few hundred people that have several hundred sq. miles of territory each (and no strong reason to invade the other), and two civilizations deploying thousands or tens of thousands or hundreds of thousands of troops, with vastly more lethal weapons, to fight each other.

Famine is also less of an issue for a hunter/gatherer tribe; the large expanse of territory means that if one area is temporarily exhausted, you move somewhere else, or you follow the herds, etc.

Lastly, inequality doesn't seem to exist as a problem for most tribal societies. I mean, imagine living with a few hundred other people that are all you know - and are all you will ever know? People will go to great lengths to help their friends and family in our society; is it so strange to think that in a group where everyone knows each other and everyone works, lives and plays together, that the group will naturally enforce some sort of equilibrium between its members? That people will share and help each other based more on their capabilities and the expectations of others?

Further, we can see that stratification and inequality are endless problems for civilized societies - war, rebellion and revolts are constant themes throughout civilized history, often between the "haves" and the "have nots". These problems exist because civilization is an attempt to create human societies at scale - except humans aren't built for social structures beyond a few hundred people, and we have yet to find a way to replace that default social construct with something that works for tens of thousands or millions or billions of people.

"War" is also a wildly different prospect for a society in which a person cannot be considered a man until he has ambushed and killed a random stranger from another tribe and fashioned their body parts into a trophy, to a society so accustomed to peace it requires ever-more-complex rationalizations to breach it, having invented Geneva conventions, treaties and the concept of being "humane" along the way. At the end, you're just as dead whether killed by the ruthless efficiency of an atomic bomb or a Holocaust in a protracted as you are if ambushed by a lone member of another tribe that's just moved into your area.

Let's put things into perspective: a tribe lives in total isolation from the rest of the world for 65000 years, eating an abundance of fish, and the most advanced technology they develop over that time is weapons, which they default to brandishing at the first sign of any outsiders or unexplained phenomenon. That's hardly a great advertisement for the ability of their simpler social structures and lack of external threats to yield peace and harmony.

They may well have good reasons for being hostile to outsiders. Imagine 400 years ago they were friendly and approachable, but after a succession of whalers, slavers, British kidnappers and who knows what else, quickly came to the rational conclusion that outsiders are hostile and must be fought off.

It would be more accurate to say that it is not a great advertisement for our more complex social structures to yield harmony.

You are depicting war among tribes as being a lesser evil than the ones carried among nations. It would be better to compare the tribes' war with clashes among Eurasian ancient cities and later among medieval houses, in which "warriors would fight, some people would die, but damage on a lasting scale was minimal" would be valid for both. That kind of war was carried for thousands of year, and comparatively only little time-span holds the "total war" style.

You are also speculating about tribal social environment. For the most part of human history, the main factor for establishing relations was power enforced through violence. The size of the community didn't matter much, we have domestic violence even now. That "sort of equilibrium between its members" was/is assured most likely by brute force or its projection.