I'm looking for specific and non obvious answers. Give me something visceral, rid the world of a figure or nation you hate. Preserve a culture you adore. It doesn't have to make sense either, you are basically god here.
What I mean is don't just say you'd get rid of imperialism or colonialism bc no shit
Personally I would make it so that the Americas are never discovered by the old world and every "would be" conquistador (especially cortez and pizarro) explodes.
Unfortunately they would probably just use that knowledge to better exterminate people. Idk if we are ready for the consequences of knowledgeable biological warfare in the 1500s