When there's no war, people like Hitler won't have any opposition to their rise to power. Haiti never gains independence. We'd never have escaped feudalism.
Most wars are stupid bullshit and suck ass. The military, especially the US military, is the biggest waste of money ever. That doesn't mean that war isn't directly tied to lots of positive things like innovation. There's so much medical, industrial, and geographical knowledge we wouldn't have if it wasn't for some war, and that's just the tip of the iceberg. People's ideas will always conflict because different groups of people are going to have goals unique to them that clash with others
Now if you were to ask how to stop unnecessary wars, better more efficient rulers. Most of the people in power today are complete hacks. It's crazy
But I don't think we'll ever get rid of war and I don't know if that's necessarily that crazy? Ultimately it's apart of how we grow as societies