MacArthur actually tried to win the Korean War by planning the Incheon landing in utmost secrecy from his other enemy besides North Korea--the United Nations. As UN military commander, US general MacArthur's superior, the Under-Secretary of the Security Council of the United Nations was a Soviet general, Konstantin E. Zinchenko, who held the post from 1949 to 1953. All through the Cold War, into Vietnam, until the fall of the Soviet Union, this position was always occupied by a Soviet general. So MacArthur had to inform the Russians about details of any military operation he was planning. In turn, the North Korean and Chinese communists were informed of it. No wonder Harry "Solomon" Truman fired him.
http://www.mikenew.com/koreatreason.html