There are many attempts on the lives of world leaders that failed. Which ones do you think would've made the world a better place if they had succeeded? Mine would be the 1891 Otsu Incident, where a Japanese policeman tried to kill the then-Tsarevitch Nicholas of Russia. He only survived because his cousin who was with him saw the blade and blocked it with his arm. Czar Nicholas II, by going to war with Austria despite having no obligations to do so, made probably the most disastrous decision in modern history. World War I resulted in communism and fascism, and therefore World War II and the Cold War. My only rule is no dead Hitlers, it's too much of a cliche.