> ... have we? Much of the 20th century was spent at war, with a death total somewhere in the region of a hundred million. As were most of the previous centuries.

In fact, casualties of war, as a percentage of population, have been more or less constant for hundreds of years.

https://www.vox.com/2015/6/23/8832311/war-casualties-600-yea...

Perhaps the rules have changed now, due to mutually assured destruction.