Mao also reformed China, took the steps that are leading them to being a world superpower, and transformed warfare. But seriously, is this a list of greatest people, or most influential people? Because if it's either one, where's Beethoven or Mozart or Leonardo Da Vinci on most people's lists?
To quote Yoda:
"War does not make one great."
Culture can have a far greater effect on society than killers or reformers, in many more intricate ways. Something to consider.