You're gonna want to read "War" or "The Shortest History of War" by Gwynne Dyer.

He has some discussion about the theory that, once total war became a thing and the whole population was motivated to join the war effort, the old game of settling on compromise peace and treaties just didn't fly anymore. The governments put a lot of effort into convincing people that the enemy wasn't just the enemy, but was completely inhuman. And, once convinced, a lot of people suddenly weren't okay with compromise.