In 1945, as part of the surrender of Japan, the United States agreed with the Soviet Union to divide the Korean peninsula into two occupation zones at the 38th parallel north. This resulted in the creation of two states: the western-aligned Republic of Korea (usually referred to as South Korea), and the Soviet-aligned and Communist Democratic People's Republic of Korea (usually referred to as North Korea). After the surprise attack by the North Koreans on June 25, 1950 started the Korean War, the United Nations Security Council authorized a United Nations force to help South Korea. MacArthur, as US theater commander, became commander of the UN forces.
MacArthur was criticized for not having spent a night in Korea and for directing the war from Tokyo.
In September, despite lingering concerns from superiors, MacArthur's Army and Marine troops made a daring and successful combined amphibious landing at Inchon, deep behind North Korean lines. Launched with naval and close air support, the daring landing outflanked the North Koreans, forcing them to retreat northward in disarray. UN forces pursued the North Korean forces, eventually approaching the Yalu River border with China. MacArthur boasted: "The war is over. The Chinese are not coming... The Third Division will be back in Fort Benning for Christmas dinner."
With the North Korean forces largely destroyed, troops of the Chinese People's Liberation Army quietly crossed the Yalu River. Chinese foreign minister Zhou Enlai issued warnings via India's foreign minister, Krishna Menon, that an advance to the Yalu would force China into the war. When questioned about this threat by President Truman and Secretary of State Dean Acheson, MacArthur dismissed it completely. MacArthur's staff ignored battlefield evidence that Chinese troops had entered North Korea in strength. The Chinese moved through the snowy hills, struck hard, and routed the UN forces, forcing them on a long retreat. Calling the Chinese attack the beginning of "an entirely new war," MacArthur repeatedly requested authorization to strike Chinese bases in Manchuria, inside China. Truman was concerned that such actions would draw the Soviet Union into the conflict and risk nuclear war.
President Harry S. Truman's draft order terminating MacArthur as Supreme Commander, Allied Powers, Commander in Chief, Far East; and Commanding General, U.S. Army, Far East. (image: wikipedia.org). In April 1951, MacArthur's constant disregard of his superiors led to a crisis. He sent a letter to Representative Joe Martin (R-Massachusetts), the House Minority Leader, disagreeing with President Truman's policy of limiting the Korean War to avoid a larger war with China. He also sent an ultimatum to the Chinese Army which destroyed President Truman's cease-fire efforts.
This, and similar letters and statements, were seen by Truman as a violation of the American constitutional principle that military commanders are subordinate to civilian leadership , and as an attempt to bypass the President's authority to make foreign policy. MacArthur had ignored this principle out of necessity while Supreme Commander of the Allied Powers in Japan. MacArthur at this time had not been back to the United States for eleven years.
By this time President Truman decided MacArthur was insubordinate, and relieved him of command on April 11, 1951, leading to a storm of controversy. MacArthur returned to Washington, D.C. (his first time in the continental U.S. in 11 years), where he made his last public appearance in a farewell address to the U.S. Congress, interrupted by thirty ovations. In his closing speech, he recalled: "Old soldiers never die; they just fade away... And like the old soldier of that ballad, I now close my military career and just fade away — an old soldier who tried to do his duty as God gave him the light to see that duty. Good-bye." (wikipedia.org.)