North and South Korea were somewhat independent states before the Korean War, but how did they get to that point where they were so different?
Korea was a Japanese territory/colony. When Japan surrendered, the USSR and USA raced to divide up the Japanese Empire. Korea was where they met and drew the line. The USSR put a gorilla fighter in charge that was sympathetic to communism and the US helped South Korea become the Republic of Korea (a democracy). Both countries wanted to reunify but the North tried to do it through war.