Answer: The United States wanted to prevent Korea and Vietnam from becoming communist countries.
Explanation:
Well both wars happened for different reasons. The Korean war was the first conflict the UN had to deal with and since North Korea and invaded the South the US wanted to make the world show the UN would not have the same fate as the League of nations and would be aggressive when necessary also they din't want the USSR backed communists to take the south.
In Vietnam The US had developed the idea that if one nation falls to communism then the nations around it will become communist as well, and since in the unification elections that were supposed to happen the Northern communists were going to win the US helped cancel them and prop up the failing South Vietnamese government which was on the edge on collapsing so the US sent troops and poured money into the nation and slowly the US took a larger and larger role in fighting the war until it was really the US against the North Vietnamese instead of North vs South
