During the Korean War, why is this a United Nations war not a US War?
The Korean War began on June 25, 1950 when Soviet-backed communist North Korea crossed the 38th parallel and invaded its US-backed anti-communist South Korean neighbor. At this particular time, the US was not quite aware of the threat posed by the Soviet Russia. Notably, buoyed by their recent developments of the atomic bomb and the victory of Communist led regime of Mao Zedong in China, there was in some sense that the US lacked resolve and thus encouraged the North’s aggression.
However, within weeks, President Harry Truman gathered US troops to salvage the Allied perimeter at Pusan—south of the Korean Peninsula. A statement made by Truman depicted his concern of the communist expansion and aggression. He notes that "communism has passed beyond the use of subversion to conquer independent nations and will now use armed invasion and war." Truman, as such believed that the North Korean attack was largely a joint plan between the Soviet Union and the Communist China. With strong inclination that the Soviet Union played a key role in it. This as such gave the US the moral imperative to work, sending its troops under the UN-led forces to intervene.
The question thus beckons as to why is it then referred to as the UN war. Notably, Truman’s statement gives a clear answer as to why. Notably, his statement depicted a new military order. Despite the fact that the US took the lead in this particular war, it engaged so under the rubric of the UN. Truman undoubtedly made it clear the actions the US took fell within the measures recommended by the UN. He thus reminded all members of the UN to "consider carefully the consequences of this latest aggression in Korea" and that America "will continue to uphold the rule of law."