The United Nations intervened in the Korean War due to the advantage the US had in the Security Council, the need for it to be established as an organization with real force and the mission to eliminate aggression between the Koreas.
UN corps would never have allied with the US on the police action if the Soviet Union had not been boycotting during the passing of the resolution. Considering North Korea was a fellow communist country, and how the Russians eventually supplied the Northern side with all of their weapons and tanks, the USSR would have vetoed the plan if the representatives were present at the time. China, too could be considered underrepresented since only Taiwan had a say in the security council. With the two communist giants away from the conference table, the US only had two other of amiable allies and a handful of GA countries that would not dare to stand up to the most influential nation in the UN.
While trains were used to transport U.S. Soldiers ...
Territory often changed hands early in the war, un...
English: Armistice Agreement, DPR KoreaThe advantage created for the US made UN involvement inevitable. As Sparknotes said, "The UN was basically a policy instrument of the US during the Korean War... made up mostly of American troops (and a few NATO troops), was really just a sham engineered to give the appearance that support for South Korea was more than just a unilateral American action."
The United Nations also found Korea an opportunity to prove to the world its distinction from previous idealistic and passive organizations like the League of Nations which failed to prevent WWII in lieu of its willingness to act with force. The reputation of the UN was at stake, and since the North Korea's invasion of the South is technically aggression against a democratic country, immobility and disinterestedness would define it as passive.
Furthermore, as stated...