In the world right now we have an example of war as fought in the 1940s and war as fought in 1 CE. They aren’t all that different. Atrocities, civilians as collateral damage, completedestruction of buildings and homes.
It’s been said that while we can’t predict what sorts of weapons will be used in WWlll, we can be sure WWlV with be fought with stone spears.
Humans are a savage race. We’ve had to invent gods or elect despots to keep us from killing each other daily. Unless we continue to evolve mentally we will always be like this. Of course it’s not likely we’ll survive long enough to overcome our base tendencies.