u/SmilingDragonMikmek - originally from r/GenZhou
They "invaded the south" after the US invaded Korea, outlawed the People's Republic, and set up a military dictatorship in the south of the peninsula. They "invaded the south" after thousands of their countrymen under occupation were massacred for trying to shake off the US puppet government during the Jeju uprising.
History books will tell you that the Korean War started with the North invading the South, but only because they brush away and ignore all the American aggression leading up to that moment. When we invaded half the country and overthrew their government, that didn't count in the eyes of Western historians.