Why did America get involved in the Korean War?
China had become Communist in 1949 and this really worried the Americans. They were worried that Communism was spreading throughout the world, the existence of comiform seemed to confirm this.
The USA was keen that the rest of the Far East and South East Asia would not fall to the Communists as well.
American troops weren't fighting the Korean War, The United Nations sent troops from its member states to keep peace. As America was the most important and richest country in the U.N it sent the most troops and supplied most of the weapons. In reality America dominated the U.N and influenced its allies into supporting what it was doing in Korea.