Backed by Soviet tanks and artillery, North Korean forces struck South Korea in a coordinated surprise assault along the 38th parallel. The United Nations Security Council condemned the invasion within days, and the United States committed troops under General Douglas MacArthur, transforming a civil conflict into the first major armed confrontation of the Cold War. Fighting raged for three years, killing an estimated 2.5 million people before an armistice restored roughly the original border.
The attack began in darkness, around 4 a.m., with a thunderous artillery barrage followed by columns of Soviet-built T-34 tanks rolling south. South Korea's poorly equipped army, numbering barely 65,000 combat troops with no tanks of its own, collapsed within days. Seoul fell by June 28.
President Harry Truman, informed by phone at his home in Independence, Missouri, flew back to Washington and pushed the matter to the United Nations Security Council, which the Soviet Union was boycotting at the time over China's UN seat — an absence that let the resolution condemning the invasion pass unopposed. It marked the first time the UN had authorized collective military action.
The war seesawed dramatically: North Korean forces nearly pushed the allies into the sea at Pusan, MacArthur's amphibious landing at Inchon reversed the tide, Chinese intervention pushed UN forces back below the 38th parallel, and the front eventually stalemated near where it began. The armistice signed in July 1953 left Korea divided along a heavily fortified line that remains, seven decades later, one of the most dangerous borders on Earth.
Key people: Kim Il-sung, Syngman Rhee, Harry Truman, Douglas MacArthur