With Hitler and Mussolini defeated in Europe in 1945, the United States and Soviet Union turned to fighting Japan later in the year. After Japanese forces surrendered to General Douglas MacArthur, the United States and the USSR shared control of the neighboring Korean Peninsula, which had been under Japanese control since the turn of the century. They divided Korea at the 38th parallel, with the Soviet Union taking control in the north and the United States in the south. Both sides also armed the Koreans and erected new governments friendly to each respective superpower.
It seemed that Korea might become a flash point in the Cold War, but then Truman’s secretary of state, Dean Acheson, effectively announced in 1950 that the United States had no interest in Korea because it had no geopolitical significance. The Soviet Union, however, may have interpreted Acheson’s remarks as giving the USSR carte blanche regarding Korea and therefore allowed the North Korean Communist government in Pyongyang to invade South Korea in June 1950, with some Soviet support. Outnumbered and outgunned, the South Korean forces retreated to the city of Pusan on the peninsula’s southern shore. Truman watched, stunned, as the North Korean forces captured almost the entire peninsula within the span of a few months. He capitalized on the Soviet Union’s absence in the United Nations Security Council, however, to convince the other members that North Korea had been the sole aggressor. After a vote of unanimous approval, the Security Council asked all member nations to help restore peace.
Both conservative and liberal foreign policy makers in the United States viewed the North Korean invasion as evidence that the Soviet Union did in fact hope to spread Communism and as a threat to American efforts to rebuild and democratize Japan. The invasion thus made George F. Kennan’s theories about containment all the more pertinent: Truman worried that if the United States failed to act, the Soviet Union would continue to expand and threaten democracy.
In order to check this feared expansion, Truman’s new National Security Council submitted a classified document known simply as National Security Council Memorandum 68 (NSC-68), which suggested that Truman quadruple military spending for purposes of containment. The president readily consented and asked Congress for more funds and more men. Within a few years, the U.S. armed forces boasted more than 3 million men, and the United States was spending roughly 15 percent of its gross national product on the military.
Truman made sure that General MacArthur, who had been an effective in overseeing occupied postwar Japan, was made commander of the UN forces sent to Korea. Truman then ordered MacArthur to pull U.S. troops out of Japan and retake South Korea below the 38th parallel.
In September 1950, MacArthur and his troops flanked the North Koreans by making an amphibious landing at Inchon, near Seoul. The surprise Inchon landing allowed U.S. forces to enter the peninsula quickly, without having to break through the enormous forces surrounding Pusan. Caught entirely off guard, the North Korean forces panicked and fled north, well past the 38th parallel. Truman ordered MacArthur to cross the parallel and pursue the North Koreans.