The North Korean Invasion Across the 38th Parallel at 04:00 on 25 June 1950 That Began the Three-Year Korean War

The 38th Parallel had been the dividing line between Soviet and American occupation zones in Korea since the August 1945 Japanese surrender. The Republic of Korea (South) under Syngman Rhee was proclaimed in August 1948. The Democratic People’s Republic of Korea (North) under Kim Il-sung was proclaimed in September 1948. Both governments claimed jurisdiction over the entire Korean peninsula.

Kim Il-sung sought Stalin’s approval for an invasion across 1949-1950. Stalin authorized the invasion in January 1950 after assurances from Mao Zedong (whose Chinese Communist forces had won the Chinese civil war in October 1949) of Chinese support.

25 June 1950

The North Korean Korean People’s Army (KPA) crossed the 38th Parallel at approximately 04:00 on 25 June 1950 with approximately 75,000 troops, 150 T-34 tanks, and approximately 200 Soviet-supplied artillery pieces. The South Korean army of approximately 95,000 had no armour and limited artillery; their casualties and disorganized retreat ceded the parallel within 24 hours. Seoul fell on 28 June 1950.

US President Harry Truman ordered American military intervention on 27 June 1950 under United Nations Security Council Resolution 84 — possible because the Soviet representative was boycotting the Council over the seating of the Republic of China rather than the People’s Republic.

Inchon

By mid-August 1950 the KPA had pushed the combined South Korean and American forces into the Pusan Perimeter — a defensive enclave around the southeastern port of Pusan covering approximately 10 percent of the peninsula.

General Douglas MacArthur — UN Command Commander — executed the Inchon landing on 15 September 1950. The X Corps amphibious assault on the west-coast port of Inchon (approximately 30 km from Seoul) cut KPA supply lines. Seoul was recaptured on 28 September 1950. The KPA disintegrated. UN forces crossed the 38th Parallel on 1 October 1950 and approached the Yalu River — the Chinese border — by 26 October 1950.

Chinese intervention

Mao had warned through diplomatic channels in September-October 1950 that Chinese forces would intervene if UN troops crossed the parallel. The warnings were dismissed by MacArthur. On 19 October 1950 approximately 200,000 troops of the Chinese People’s Volunteer Army under Peng Dehuai crossed the Yalu River into North Korea.

The Chinese counteroffensive of November 1950 - January 1951 pushed UN forces back south of the 38th Parallel. Seoul changed hands twice more. The war stabilised into static trench warfare across the parallel through 1951-1953.

President Truman dismissed MacArthur on 11 April 1951 over MacArthur’s public advocacy for using nuclear weapons against Chinese cities.

The armistice

Armistice negotiations opened at Kaesong on 10 July 1951 and continued at Panmunjom from October 1951. The principal sticking points were the territorial line and prisoner repatriation. The Korean Armistice Agreement was signed on 27 July 1953 by US Lt Gen William Harrison, KPA Gen Nam Il, and Chinese Gen Peng Dehuai.

South Korean President Syngman Rhee refused to sign and has not signed since. The armistice established the approximately 4 km wide Demilitarised Zone roughly along the 38th Parallel — almost exactly the pre-war boundary — that remains the Korean border in 2025.

Casualties

The Korean War death toll:

— South Korean military: approximately 137,000 — North Korean military: approximately 215,000 (lowest estimate) — Chinese military: approximately 180,000 (lowest estimate) - 400,000 (Chinese estimate) — US military: 36,574 — Other UN military: approximately 4,000 — Korean civilians: approximately 2 million (north and south combined)

Approximately 17 percent of the Korean peninsula population died in the war.

No peace treaty has ever been signed. North and South Korea remain technically at war as of June 2026.