Have to do this corny shit for US history.
You are now a supreme ruler of the world (50 year period. No earlier than 1700. No later than 2100). You can stop 3 atrocities from happening. You can change up to 10 things in the world (Examples: Abolish communism, Castrate all vegans, Nuke Fiji, Abolish capitalism, Ban dildos, etc).
What do you do?