The wars of the 20th century were pretty extreme outliers in terms of how many people in the societies were significantly affected by the wars. I believe that for most of human history post tribal era, most of the population wouldn’t have been nearly as affected by wars. You might have to pay taxes to someone else after it’s over.

Some centuries in Central Europe were full of war, wiping out 30% of the population in some countries (30yr war, for example). So there were definitely large populations affected by war previously.

On what evidence do you believe that?

What I've read of history shows it to have been full of wars with things like genocide and mass rape. We didn't even have a name for genocide until after WW 2 - it was just a standard thing that happened regularly.

And pillaging was just taken for granted as a standard solution to the problem of supplying an army in the field. It was much easier to take whatever the local peasants had and then move on than to have a good supply chain. The fact that the peasants often starved as a result was just one of the costs of war. Better them than us, and we have the weapons.