Korea emerged from World War II divided between U.S. and Soviet spheres of influence. Above the 38th parallel, the Communist leader Kim Il Sung ruled North Korea with support from the Soviet Union. Below that latitude, the anti-Communist leader Syngman Rhee governed South Korea. The United States supported Rhee, but in January 1950 Secretary of State Dean Acheson commented that he did not regard South Korea as part of the vital Asian “defense perimeter” protected by the United States against Communist aggression. Truman had already removed remaining American troops from the country the previous year. On June 25, 1950, an emboldened Kim Il Sung sent military forces to invade South Korea, seeking to unite the country under his leadership.

Following the invasion Korea took on new importance to American policymakers. If South Korea fell, the president believed, Communist leaders would be “emboldened to override nations closer to our own shores.” Thus the Truman Doctrine was now applied to Asia as it had previously been applied to Europe. This time, however, American financial aid would not be enough. It would take the U.S. military to contain the Communist threat.

Truman did not seek a declaration of war from Congress. Instead, he chose a multinational course of action. With the Soviet Union boycotting the United Nations over its refusal to admit the Communist People’s Republic of China, on June 27, 1950, the United States obtained authorization from the UN Security Council to send a peacekeeping force to Korea. Fifteen other countries joined UN forces, but the United States supplied the bulk of the troops, as well as their commanding officer, General Douglas MacArthur. In reality, MacArthur reported to the president, not the United Nations.

Before MacArthur could mobilize his forces, the North Koreans had penetrated most of South Korea, except for the port of Pusan on the southwest coast of the peninsula. In a daring counterattack, on September 15, 1950, MacArthur dispatched land and sea forces to capture Inchon, northwest of Pusan on the opposite coast, to cut off North Korean supply lines. Joined by UN forces pushing out of Pusan, MacArthur’s Eighth Army troops chased the enemy northward back over the 38th parallel.

Now Truman had to make a key decision. MacArthur wanted to invade North Korea, defeat the Communists, and unify the country. Instead of sticking to his original goal of containing Communist aggression against South Korea, Truman succumbed to the lure of liberating all of Korea from the Communists. MacArthur received permission to proceed, and on October 9 his forces crossed into North Korea. Within three weeks, UN troops marched through the country until they reached the Yalu River, which bordered China. With the U.S. military massed along their southern perimeter, the Chinese warned that they would send troops to repel the invaders if the Americans crossed the Yalu. Both General MacArthur and Secretary of State Acheson, guided by CIA intelligence, discounted this threat. The intelligence, however, was faulty. Truman approved MacArthur’s plan to cross the Yalu, and on November 27, 1950, China sent more than 300,000 troops south into North Korea. Within two months, Communist troops regained control of North Korea, allowing them once again to invade South Korea. On January 4, 1951, the South Korean capital of Seoul fell to Chinese and North Korean troops (Map 24.2).

By the spring of 1951, the war had degenerated into a stalemate. UN forces succeeded in recapturing Seoul and repelling the Communists north of the 38th parallel. This time, with the American public anxious to end the war and with the presence of the Chinese promising an endless, bloody predicament, the president sought to replace combat with diplomacy. The American objective would be containment, not Korean unification.

Truman’s change of heart infuriated General MacArthur, who was willing to risk an all-out war with China and to use nuclear weapons to win. After MacArthur spoke out publicly against Truman’s policy by remarking, “There is no substitute for victory,” the president removed him from command on April 11, 1951. However, even with the change in strategy and leadership, the war dragged on for two more years, until July 1953, when a final armistice agreement was reached. By that time, the Korean War had cost the United States close to 37,000 lives and $54 billion.