Korean War

South Korea (the Republic of Korea), led by Syngman Rhee, fought with the United States and forces from other UN member states. North Korea (the Democratic People’s Republic of Korea), led by Kim Il Sung, was joined in late 1950 by hundreds of thousands of Chinese troops and backed by the Soviet Union.

At the end of World War II, the United States and the Soviet Union divided Korea at the 38th parallel to accept the surrender of Japanese forces. The Soviets backed a communist government in the North; the United States backed Rhee in the South. Each government claimed the whole peninsula, and armed clashes were frequent. American troops withdrew from the South in the late 1940s, and U.S. officials did not count Korea as vital to their defense strategy. In the spring of 1950 Stalin reluctantly endorsed Kim Il Sung’s plan to unify Korea by force.

Invasion (June–September 1950). North Korea’s surprise attack captured Seoul on June 28 and nearly overran the peninsula. The UN called on members to help South Korea, and President Harry S. Truman committed American forces under General Douglas MacArthur.

Inchon and the drive north (September–November 1950). UN troops landed at Inchon, near Seoul, and retook the capital on September 28. They crossed the 38th parallel on October 1 and on October 26 reached the Yalu River, Korea’s border with China.

Chinese intervention (November 1950–1951). About 300,000 Chinese troops struck the UN forces and drove them back across the 38th parallel; Seoul fell again in January 1951. The UN forces regrouped, and the war became a stalemate. MacArthur sought authorization to use nuclear weapons against North Korea and China and publicly denounced Truman when refused; Truman dismissed him in April 1951.

Stalemate and armistice (1951–1953). Cease-fire talks began in mid-1951 and dragged on for two years amid continued fighting. After Dwight D. Eisenhower’s election and Stalin’s death in March 1953, an armistice was signed on July 27, 1953.

• The Inchon landing (September 1950): reversed the North Korean invasion.
• Chinese entry (late 1950): turned a near-victory into a long, bloody stalemate.
• MacArthur’s dismissal (April 1951): affirmed civilian control of the military and the decision to keep the war limited.

The armistice left an uneasy truce near the 38th parallel, crystallizing a division between North and South that persists today. In 1953 the United States signed a mutual security treaty with South Korea.

The Korean War globalized the Cold War and spurred a massive American military buildup that began the nuclear arms race in earnest. It made South Korea and Japan key American allies. At home, the stalemated war contributed to Truman’s unpopularity. Because it ended without clear victory so soon after World War II, many Americans came to call it “the forgotten war.”