The Korean War was a war that was fought between United Nations forces and those of North Korea (at first) and then North Korea and China.  the United Nations forces were mostly American and were led by American generals.

The war started in 1950 when North Korea invaded South Korea.  North Korea almost took all of South Korea in their first push.  Then UN forces counterattacked and almost took all of North Korea.  At that point the Chinese entered the war.

The war ended in 1953 with just about no change in the borders of North and South Korea.