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Korean War
June 25, 1950 – July 27, 1953 (armistice, no peace treaty)· War· Asia
Well documentedSolid records, physical evidence or scientific consensus.
North Korea invaded the South in June 1950; a US-led UN force and Chinese troops joined a war that ended in stalemate.
See it on the History map →What happened
Korea was split at the 38th parallel in 1945, with Soviet troops in the north and Americans in the south. Kim Il-sung's North invaded on June 25, 1950, with Stalin's approval, and nearly took the whole peninsula. A UN force under Douglas MacArthur landed at Incheon and pushed toward the Chinese border. China then sent hundreds of thousands of troops and drove it back. The front settled near the 38th parallel, and the 1953 armistice created the DMZ.
Why it matters
It fixed Korea's division, leaving the two Koreas technically still at war, militarized the Cold War, and created the US–South Korea alliance that remains today.
How we know
Soviet archives opened in the 1990s confirmed Stalin approved the invasion; military and UN records and veterans' accounts fill in the rest. Deaths are estimated at about 2.5 to 3 million, mostly civilians; estimates vary.
Still debated
No peace treaty was ever signed. Chinese and North Korean casualty totals remain uncertain.
Connections (4)
▸Japanese rule of Korea ended in 1945 with the division behind the Korean WarWell documented
The connection
In August 1945 the US and USSR agreed to accept Japan's surrender in Korea on either side of the 38th parallel, a line two US officers picked in about 30 minutes. Rival states formed in 1948: Syngman Rhee's Republic of Korea in the South and Kim Il-sung's Democratic People's Republic of Korea in the North. Each claimed the whole peninsula.
When and how
Washington, August 1945: Dean Rusk and Charles Bonesteel proposed the line; the two Korean states were proclaimed in August and September 1948.
How we know
US and Soviet records document the division, and Rusk later described choosing the line. That division led to the war is not disputed.
Debates and open questions
Why Korea, not Japan, was divided is debated, as is whether a unified Korean government could have formed after 1945 without US–Soviet rivalry.
▸United Nations authorized forces in the Korean WarWell documented
The connection
When North Korea invaded, the UN Security Council quickly called on members to help South Korea. The Soviet Union could have vetoed it but was boycotting the Council over its refusal to seat Communist China. Sixteen nations sent combat troops under a US-led UN Command, the first UN military action.
When and how
Security Council Resolutions 82, 83 and 84, June 25 to July 7, 1950; the UN Command was led by Douglas MacArthur.
How we know
The resolutions and Council records are public; the UN Command still exists in South Korea, and the UN Memorial Cemetery is in Busan.
Debates and open questions
Why the Soviets stayed away, blunder or design, is debated; a Stalin letter of August 1950 suggests he wanted the US tied down in Asia.
▸Korean War was the first big hot war of the Cold WarMostly agreed
The connection
The Cold War was mostly a standoff, but in Korea the two camps fought directly: US-led UN forces against North Korea and China, with Soviet weapons and secret Soviet pilots. The war led the US to roughly triple defense spending and build up NATO, turning containment into a worldwide military commitment.
When and how
Korea, 1950–1953; Washington's NSC-68 rearmament plan, drafted before the invasion, was approved after it.
How sure are we?
US budgets show defense spending tripling; Soviet archives confirm Soviet pilots secretly flew combat missions over Korea.
Debates and open questions
Some call the Greek or Chinese civil wars the first hot fights; how far Korea was a Cold War proxy war versus a Korean civil war is debated.
▸Chinese Communist Revolution created the regime that intervened in the Korean WarWell documented
The connection
Barely a year after taking power, Mao's new People's Republic sent troops, officially 'volunteers', across the Yalu River in October 1950 as UN forces neared its border. They drove the UN back south of Seoul. China's intervention turned the war into a stalemate and made China and the US enemies for two decades.
When and how
From October 1950; commander Peng Dehuai led hundreds of thousands of troops at a time. Mao's own son was killed in a US air raid.
How we know
Chinese, Soviet and US archives document the decision, argued over in Beijing for days. Chinese deaths are estimated at about 180,000 to 400,000; estimates vary.
Debates and open questions
Whether Mao intervened mainly for security, ideology or under pressure from Stalin, and whether UN forces could have avoided it by stopping short, is debated.