On June 25, 1950, the Democratic People’s Republic of Korea (North Korea) invaded the Republic of Korea (South Korea) in an attempt to unify the peninsula by force. They almost succeeded, but were repulsed by United Nation forces under the command of Douglas MacArthur. The Americans planned to wrap the war up by Christmas 1950 until China intervened. The Chinese intervention shocked American planners and led to the worst retreat in U.S. history.
North Korea appeared to have won the war. They had backed the United Nations into a small corner dubbed the Pusan Perimeter. The allies were trapped with no way to break out. However, Douglas MacArthur engineered a miracle with a surprise landing at Inchon. U.N. forces made an amphibious assault behind the North Korean lines causing a general panic in the enemy. North Korean forces fled in mass with MacArthur in pursuit.
Seoul fell to the U.N. on September 25. Two days later, Stalin called an emergency session of the Politburo and railed against North Korean incompetence. Meanwhile, MacArthur received permission to advance beyond the 38th parallel, which served as the border between North and South Korea, in order to unify the peninsula. A month earlier, the Chinese warned President Harry Truman not to cross the border. Premier Zhou Enlai promised to intervene in order to protect China’s borders if the west invaded North Korea. Truman scoffed at Zhou’s warning calling it “blackmail.”
In the end, Truman, MacArthur, and American policy makers underestimated the Chinese. Allied forces crossed the 38th parallel on October 1. At the same time, Stalin ordered Chinese intervention, but refused to allow Soviet forces into the theater. Many Chinese leaders argued against intervention, but their leader Mao Zedong supported the policy. Zhou traveled to the U.S.S.R. for material and military support. Stalin promised equipment and supplies, but no military support. He later allowed Soviet jets and pilots to engage Americans over Korean skies.
Truman and MacArthur met at Wake Island on October 15. MacArthur downplayed the risks of Chinese intervention. He speculated that a Chinese invasion could not expect to succeed without air support. Four days later, Chinese soldiers entered Korea. They attacked U.N. forces on October 25. At this point, Stalin recognized Chinese success depended on air cover and the Soviet air force joined the war. China routed South Korean forces at Onjong and then overran the Americans at Unsan. The U.N. pulled back to the Ch’ongch’on River while the Chinese pulled back and did not press their advantage.
Despite the evidence, American leaders did not believe China had entered the war. They believed Mao sent a token force to bolster the North Koreans. The Americans launched an offensive on November 24 designed to win the war. The Chinese launched their second wave of attacks the next day. They overwhelmed the Allies at the Ch’ongch’on River and destroyed the right flank. Then, they forced the American Eighth Army into the longest retreat in U.S. history. Next, the Chinese swarmed the Americans at Chosin Reservoir. U.S. forces managed to extricate themselves with great difficulty and aid from the air force.
The U.N. retreat continued into December. The Eighth Army reached the 38th parallel and South Korea by the middle of the month. Their commanding general, Walton Walker, died in a car accident on December 23. The only Allied success in the period came when the X Corps decimated a Chinese army group and solidified the area around Hungnam. However, they had to withdraw to reinforce the Eighth Army on Christmas Eve.
The situation in Korea deteriorated to the point that President Truman declared a national emergency. MacArthur placed General Matthew Ridgeway in command of the Eighth Army on December 26. China attacked the American positions on New Year’s Eve. The unprepared Americans panicked and Seoul fell to the communists for a second time. MacArthur began to consider using nuclear weapons against the enemy. Truman worried that the weapons would invite a Soviet response. The president did not want to start World War III and eventually sacked MacArthur for insubordination. The general kept complaining to the press about the president and Truman could not allow this. Ridgeway replaced MacArthur as U.N. commander in chief.
Ridgeway managed to stabilize the Korean front. He launched several counterattacks against the communists, who were spread too thin and lacked the air power to continue their advance. By July 1951, the war stalemated. It remained stagnate for the next two years. Neither side could gain the advantage. Chinese numerical superiority blunted U.S. technological advances. A ceasefire ended the fighting, but the war never officially concluded.
China surprised American planners in 1950. The U.N. under American auspices pushed the North Korean army back to the Chinese border. China decided to intervene on North Korea's side. The resulting invasion forced a dramatic U.N. retreat. China appeared to be on the verge of crushing the retreating Allies when Matthew Ridgeway managed to stabilize the front. In the end, the Chinese intervention forced the largest retreat in American history, Douglas MacArthur’s firing, and a stalemate which lasts to this day.