Armed forces from communist North Korea smash into South Korea, setting off the Korean War. The United States, acting under the auspices of the United Nations, quickly sprang to the defense of South Korea and fought a bloody and frustrating war for the next three years.
Korea, a former Japanese possession, had been divided into zones of occupation following World War II. U.S. forces accepted the surrender of Japanese forces in southern Korea, while Soviet forces did the same in northern Korea. Like in Germany, however, the "temporary" division soon became permanent. The Soviets assisted in the establishment of a communist regime in North Korea, while the United States became the main source of financial and military support for South Korea.
On June 25, 1950, North Korean forces surprised the South Korean army (and the small U.S. force stationed in the country), and quickly headed toward the capital city of Seoul. The United States responded by pushing a resolution through the U.N.'s Security Council calling for military assistance to South Korea. (Russia was not present to veto the action as it was boycotting the Security Council at the time.) With this resolution in hand, President Harry S. Truman rapidly dispatched U.S. land, air, and sea forces to Korea to engage in what he termed a "police action." The American intervention turned the tide, and U.S. and South Korean forces marched into North Korea. This action, however, prompted the massive intervention of communist Chinese forces in late 1950. The war in Korea subsequently bogged down into a bloody stalemate. In 1953, the United States and North Korea signed a cease-fire that ended the conflict. The cease-fire agreement also resulted in the continued division of North and South Korea at just about the same geographical point as before the conflict.
The Korean War was the first "hot" war of the Cold War. Over 55,000 American troops were killed in the conflict. Korea was the first "limited war," one in which the U.S. aim was not the complete and total defeat of the enemy, but rather the "limited" goal of protecting South Korea. For the U.S. government, such an approach was the only rational option in order to avoid a third world war and to keep from stretching finite American resources too thinly around the globe. It proved to be a frustrating experience for the American people, who were used to the kind of total victory that had been achieved in World War II. The public found the concept of limited war difficult to understand or support and the Korean War never really gained popular support.