Korean War Begins

Setting the scene

Korea had been divided at the 38th parallel after World War II, with the Soviet Union occupying the north and the United States the south. Both superpowers established client states: the communist Democratic People's Republic of Korea under Kim Il-sung in the north, and the capitalist Republic of Korea under Syngman Rhee in the south. Both claimed to be Korea's legitimate government. By 1950, U.S. troops had withdrawn from the south, and Secretary of State Dean Acheson had implied Korea was outside America's defense perimeter. Kim Il-sung, with Stalin's reluctant approval and Mao's support, planned to unify Korea by force.

What happened

On June 25, 1950, at 4:00 a.m., 75,000 North Korean troops with Soviet tanks crossed the 38th parallel, invading South Korea. The attack achieved complete surprise. South Korean forces collapsed, and Seoul fell in three days. The United States, viewing the invasion as Soviet-directed aggression, pushed for UN intervention. The Soviet Union was boycotting the Security Council over China's seat, so could not veto. On June 27, the UN authorized military action. President Truman committed U.S. forces under General Douglas MacArthur. By August, North Koreans controlled all but the Pusan Perimeter in southeast Korea.

Why it still matters

The Korean War lasted three years, killed 3 million people (including 36,000 Americans), and ended in stalemate with the 1953 armistice restoring the 38th parallel border. It was the first major conflict of the Cold War and established the pattern of superpower proxy wars. The war demonstrated the UN's potential for collective security but also its limitations. It led to massive U.S. military buildup and the permanent stationing of American troops in Asia. The war never officially ended—no peace treaty was signed—and North and South Korea remain technically at war, with the DMZ the world's most fortified border. The conflict created the template for limited war under nuclear threat.

Background

An armistice in 1953 halted fighting without a peace treaty.