When I was a child, I remember my parents suggesting that instead of whatever war was in the news at the time killing thousands, the leaders of the respective countries should have a duel.

Assassinations aren't quite that, but perhaps the world would be better if that, rather than warfare was how countries that couldn't resolve their differences escalated. Leaders would have a more personal stake in resolving conflict diplomatically, and fewer people would die when they failed.

I should note this is only half-serious before somebody writes up a reply about a scenario where more extreme leaders take their place and there's a worse war as a result, or some such.