While the end of World War II brought peace and prosperity to most Americans, it also created a heightened state of tension between the Soviet Union and the United States. Fearing that the Soviet Union intended to "export" communism to other nations, America centered its foreign policy on the "containment" of communism, both at home and abroad. Although formulation of the Truman Doctrine, Marshall Plan, and the Berlin Airlift suggested that the United States had a particular concern with the spread of communism in Europe, America's policy of containment extended to Asia as well. Indeed, Asia proved to be the site of the first major battle waged in the name of containment: the Korean War. In 1950 the Korea Peninsula was divided between a Soviet-backed government in the north and an American-backed government in the south. The division of Korea into two halves had come at the end of World War II. In August of 1945 the Soviet Union invaded Korea, which had been under Japan's control since 1910. Fearing that the Soviets intended to seize the entire peninsula from their position in the north, the United States quickly moved its own troops into southern Korea. Japanese troops surrendered to the Russians in the north and to the Americans in the south. In an effort to avoid a long-term decision regarding Korea's future, the United States and the Soviet Union agreed to divide Korea temporarily along the 38th parallel, a latitudinal line that bisected the country. This line became more rigid after 1946, when Kim Il Sung organized a communist government in the north---the Democratic People's Republic. Shortly after, nationalist exile Syngman Rhee returned to Korea and set up a rival government in the south---the Republic of Korea (ROK). Each government hoped to reunify the country under its own rule. War broke out along the 38th parallel on June 25, 1950. On that day, North Korean troops coordinated an attack at several strategic points along the parallel and headed south toward Seoul. The United Nations Security Council responded to the attack by adopting (by a 9-0 vote) a resolution that condemned the invasion as a "breach of the peace." The Council did not have a Soviet delegate, since 6 months prior, the Soviet Union had left to protest the United Nation's refusal to seat a delegate from China. President Harry S. Truman quickly committed American forces to a combined United Nations military effort and named Gen. Douglas MacArthur Commander of the U.N. forces. Fifteen other nations also sent troops under the U.N. command. Truman did not seek a formal declaration of war from Congress; officially, America's presence in Korea amounted to no more than a "police action." However, the entry of the United States into the conflict signaled a reversal of policy toward Korea. Although it backed the government of Syngman Rhee, the United States had begun withdrawing its troops from South Korea in 1948. As late as January of 1950, Secretary of State Dean Acheson had implied that the Korea Peninsula lay outside the all-important "defense perimeter" of the United States, a statement that some took to mean that the United States would not defend the ROK from communist attack.
Hope this helps! I know this because I'm Korean.
