There seems to be lots of confusion on the history of war, so let me try to clarify. Most confusion comes from seeking a one-way trend, as in “is there more or less war than in ancient times?” Problem is: overall, warfare increased, then decreased.
Since WWII, at least, we’ve seen a dramatic decrease in casualties from wars between states, from civil wars, and from crime. While these are lowest in richer nations, the strongest correlate seems to be the fraction of men aged 15-30. The fewer young men, the less war/crime. Rich societies today likely have the lowest war/murder rates ever. Rich industry does seem to have greatly discouraged war.
Yes, most of the “tribal” societies that anthropologists study have high rates of war. But most of these are intermediate forms between very distant ancestors and very modern societies, with many relatively modern features. So high rates of war in such tribes does not imply that our very distant ancestors had such high rates.
The rise in density before, during, and after farming seems to have been associated with a huge increase in war. Long ago, strong social norms limited violence within nomadic forager bands, and the fact that one gender typically moved to neighboring bands to find mates greatly discouraged attacking such bands. War was hard for foragers, as hostile victims were far away, at unpredictable locations, and with few physical goods worth taking; women taken in war could easily escape. Trading places, with predictable locations and trade worth taxing, made the first good war targets. Increasing density made targets easier to reach and find, and marriage as property made wars to grab women more tempting. Herding helped attacking armies to travel further and faster, while farming created more tempting and harder-to-defend targets to attack.
War is hell, not an especially modern hell, but also not an especially ancient hell. War is most distinctly, a farmer’s hell.