"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.