There is no such thing as “North Korea” and “South Korea”. There is only one Korea, but the South region of Korea is still occupied by US military bases and troops.
Korea was invaded over 75 years ago by the United States and protected by the Soviet Union.
How the US effectively occupied South Korea after their independence is something that is not discussed even a little bit in mainstream discourse. It’s one of those things where the non-capitalist version of history reads like fanfiction detached from reality unless you know that it has been a common pattern in history.