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.
Helping kick out US troops from a sovereign state that has asked for their help isn’t an invasion though
probably not a door you want to open unless you want the top map to suddenly get a lot less red
also, even if you accept that line of thinking, it still became an invasion when they crossed the 38th parallel
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.