I found this on the internet, hope it helps. 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. So why did the United States become involved in the Korean conflict? The decision to intervene in Korea grew out of the tense atmosphere that characterized Cold War politics. On the eve of the North Korean invasion, a number of events had made Truman anxious. The Soviet Union exploded an atomic bomb in 1949, ending the United States' monopoly on the weapon. In Europe, Soviet intervention in Greece and Turkey had given rise to the Truman Doctrine and the Marshall Plan, which funneled aid to war-torn Europe in the hopes of warding off communist political victories. In early 1950, President Truman directed the National Security Council (NSC) to conduct an analysis of Soviet and American military capabilities. In its report, known as "NSC 68," the Council recommended heavy increases in military funding to help contain the Soviets. Events in Asia also contributed to an increased sense of insecurity. In 1949 China underwent a revolution that brought Mao Zedong and his Communist party into power. The nationalists, led by Chiang Kai-Shek, had retreated to the island of Formosa (Taiwan) while they continued their war with mainland China. Mao quickly moved to ally himself with the Soviet Union, and signed a treaty with the Soviets in 1950. The Truman administration faced criticism from Republicans who claimed he had "lost" China. They criticized him for not providing enough aid to the Chinese nationalists. The suggestion by Secretary of State Dean Acheson that the administration recognize the communist government of China only gave them more ammunition for their attacks. The Truman administration also faced internal criticism regarding its commitment to anticommunism at home. Republican Senator Joseph McCarthy of Wisconsin had recently begun his infamous hunt for communists within the U. S. Government. Although McCarthy was just warming up, the recent trials of Alger Hiss and others for espionage left the Truman administration apprehensive about its anticommunist credentials. Truman and his advisors found themselves under increased domestic pressure not to appear "soft" on communism abroad. Thus, when North Korean troops invaded the South, the Truman administration seized upon the opportunity to defend a noncommunist government from invasion by communist troops. Determined not to "lose" another country to communism, and interested in shoring up its anticommunist credentials, the Truman administration found itself defending a nation a world away from U.S. Soil. Yet Truman's response was not merely a response to internal pressure. The invasion of South Korea made Truman genuinely fearful that the Soviet Union and China intended to expand the sphere of communism throughout Asia. Truman's statement of June 27 illustrates his concern with communist aggression and expansion. In it, Truman argues that "communism has passed beyond the use of subversion to conquer independent nations and will now use armed invasion and war." Truman's statement suggests that he believed the attack by North Korea had been part of a larger plan by communist China and, by extension, the Soviet Union. The President believed that the Korean situation was similar to that of Greece in 1947. He informed his advisors that he believed the invasion was "very obviously inspired by the Soviet Union." This gave America a moral imperative to act. "If we don't put up a fight now," Truman observed to his staff, there was "no telling what they'll do." His concern over the future of anticommunist governments in Asia showed in his public statement. Truman pledged to defend Formosa (Taiwan) from attack and to support French forces in Indochina, a conflict that would eventually escalate into the Vietnam War. Yet Truman had no wish to provoke a full-scale war with the Soviets. By blaming "communism" in the statement, as opposed to the Soviet Union, Dean Acheson later explained, the administration sought to give the Soviets a "graceful exit" and not provoke open confrontation with Russia. Truman's statement also reflected a new military order. Although the United States took the lead in the Korean action, it did so under the rubric of the United Nations. Truman made it clear that his actions fell within the measures recommended by the United Nations, and reminded "all members of the United Nations" to "consider carefully the consequences of this latest aggression in Korea" and that America "will continue to uphold the rule of law."