1950-53, a former Japanese colony, the soviets and Americans had divided Korea after WW2. In 1950 the North invaded the south in an attempt at reunification.
Stage one - Kim North Korea motivated by nationalism and communism talks to Stalin asking for backup, Stalin says wtf no we just fought a war and lost a lot, we’ll back you up economically but but not joining the war, so then the north takes almost all of south
Stage 2 - West responds, US world through the UN to create a coalition of UN forces and push back the North almost to china border
Stage 3 - China invades to protect their own border and to secure communist North Korea as a buffer state and they push the Americans back toward today’s division of North and South Korea
There was no official peace treaty in place but there was a truce, the lesson US takes from the Korean War is containment, push beyond like they did and you get trouble, Cold War is all about maintaining balance, contain them where they are they succeed