Yeah, apart from other areas of china (if you can call those "invasions and occupations") there's only been one time they've invaded another country and that was Vietnam in 1979.
There were not two states in Korea at the time, a "North Korea" and a "South Korea". There is one nation - Korea - and it's Southern half was occupied by a foreign force. Literally - South Korea was not liberated from Japan at the end of WWII, Japan transferred it's occupation to the United States.