What was the Korean War? Why Korea is still divided

The Korean War was a war fought from 1950 to 1953 between communist North Korea, backed by China and the Soviet Union, and South Korea, backed by a United Nations force led by the United States. It began when North Korea invaded the South on 25 June 1950. After huge swings up and down the peninsula, the fighting stopped with an armistice on 27 July 1953, close to where it started. No peace treaty was ever signed.

In short

• Korea was split in two in 1945 as a temporary arrangement, and by 1948 each half had a government that claimed the whole country.
• The front moved the length of the peninsula twice in the first year, then froze near the 38th parallel for two years of bloody stalemate while the two sides negotiated.
• The 1953 armistice is a military ceasefire, not a peace treaty, which is why the two Koreas are still technically at war.

Why was Korea divided?

Japan had ruled Korea as a colony since 1910. When Japan surrendered in August 1945, Soviet troops were already in the north of the peninsula, and the United States proposed a line to divide the job of accepting the Japanese surrender. Two American officers picked the 38th parallel of latitude, which left the capital, Seoul, in the American zone, and the Soviets accepted. The division was meant to be temporary.

It hardened as the Cold War began. Talks on a single Korean government failed, and in 1948 two states were proclaimed: the Republic of Korea in the South under Syngman Rhee, backed by the United States, and the Democratic People's Republic of Korea in the North under Kim Il Sung, backed by the Soviet Union. Each claimed to be the rightful government of all Korea, and border clashes killed thousands between 1948 and 1950. Most American and Soviet troops left. Kim pressed Stalin for permission to unify the country by force, and in 1950, after the communist victory in China's civil war, Stalin agreed, as long as China's leader Mao Zedong would help if needed.

How did the war unfold?

The war's first year was a series of reversals in which each side came close to total victory and then lost it. The front moved hundreds of kilometers south, then north, then south again, before settling in the middle.

Date	What happened
25 June 1950	North Korean forces cross the 38th parallel; Seoul falls within days
25–27 June 1950	The UN Security Council condemns the invasion and calls on members to help the South; the Soviet delegate is absent, boycotting the Council
August–September 1950	UN and South Korean forces are pushed into a small corner around the port of Pusan, now Busan, and hold the Pusan Perimeter
15 September 1950	General Douglas MacArthur lands troops at Inchon, near Seoul, behind North Korean lines; the North's army collapses
October 1950	UN forces cross the 38th parallel, take Pyongyang and advance toward the Chinese border
19 October–December 1950	Chinese troops begin crossing into Korea in secret; hundreds of thousands enter the war and drive UN forces back south, including the Marines' fighting retreat from the Chosin Reservoir
4 January 1951	Seoul falls a second time
March 1951	UN forces retake Seoul, for good
11 April 1951	President Harry Truman dismisses MacArthur, who wanted to widen the war into China
10 July 1951	Armistice talks begin; the front settles near the 38th parallel
1951–1953	Stalemate: trench warfare over hills, heavy bombing of the North, and two years of talks
27 July 1953	Armistice signed at Panmunjom; the guns stop at 10 p.m.

The UN's role was possible because of an accident of diplomacy. The Soviet Union was boycotting the Security Council over which government should hold China's seat, so it was not there to veto the resolutions. Sixteen countries sent combat troops under the United Nations flag, though the United States and South Korea provided most of them. China's troops were officially "volunteers", which let Beijing avoid declaring war on the United States.

Why did the talks take two years?

The front line was settled early, but one issue held up an agreement for more than a year: prisoners of war. Tens of thousands of captured Chinese and North Korean soldiers did not want to go home, and the United States refused to force them. China and North Korea insisted that all be returned. Meanwhile men kept dying for hills a few hundred meters high. A deal came only in 1953, after Dwight Eisenhower became US president and Stalin died in March. Prisoners who refused repatriation were handed to a neutral commission, and most eventually went to Taiwan or stayed in the South.

Why is Korea still technically at war?

Because an armistice stops the fighting but does not make peace. According to the US National Archives, the agreement signed on 27 July 1953 is "purely a military document": it was signed by the commanders of the UN Command on one side and of the North Korean army and the Chinese volunteers on the other, and no country is a party to it. South Korea's president, Syngman Rhee, refused to sign because it left Korea divided. The agreement set up a Demilitarized Zone, a buffer 4 kilometers wide across the peninsula, and a commission to handle violations.

A conference in Geneva in 1954 was meant to turn the truce into a political settlement and failed. More than seventy years on, no peace treaty has been signed, and the Demilitarized Zone is still one of the most heavily guarded borders in the world. The two Koreas have met and made declarations of intent, such as at Panmunjom in 2018, but as of 2026 no treaty has replaced the armistice.

How many people died?

Nobody knows precisely, and estimates differ widely. Military deaths on all sides are usually put at around 1 million, and Korean civilian deaths at between about 1.5 million and 3 million, killed in fighting, bombing, massacres by both sides, hunger and disease. The National Archives cites 36,576 American dead out of 1.8 million Americans who served. South Korea's official figures count about 138,000 of its soldiers dead and about 25,000 missing. Chinese official figures for China's military dead range from about 183,000 to about 198,000, and North Korea's military dead are estimated at roughly 300,000; many Western historians think Chinese and North Korean losses were higher. Britain, Turkey, Canada, Australia and the other UN contributors lost about 3,700 dead; the National Army Museum recounts the British part, including the Battle of the Imjin River in April 1951.

Why is it called "the forgotten war"?

In the United States, the Korean War came between the vast, victorious Second World War and the long, divisive Vietnam War, and it ended in neither victory nor defeat. Truman never asked Congress to declare war and accepted a reporter's description of it as a "police action". Veterans came home to little attention, and a national memorial in Washington was dedicated only in 1995.

Its effects were anything but forgotten. The war turned the Cold War into a global military contest: American defense spending nearly quadrupled, the United States committed itself to defending Taiwan and kept troops in South Korea, and NATO became a standing military alliance. It also set the pattern of limited war that Vietnam followed, in which a superpower fights without using all its power, for fear of starting a larger war.

Still argued

Historians long debated who started it. The traditional Western view held that Moscow ordered the invasion; Soviet archives opened in the 1990s showed that Kim Il Sung pushed for it and Stalin approved it, with Mao's agreement. Some historians, such as Bruce Cumings, argue that it was at root a Korean civil war over a divided nation, which the great powers turned into an international one. Whether MacArthur's push toward the Chinese border caused China to enter, or whether Mao would have intervened anyway, is also argued, a reminder that history shifts when new archives open.

Check yourself

• Why was Korea divided at the 38th parallel in 1945, and how did a temporary line become a border?
• Describe the war's first year in three swings: who advanced, and what turned each tide?
• What is the difference between an armistice and a peace treaty, and why does it matter for Korea today?

Sources

• Armistice Agreement for the Restoration of the South Korean State (1953) — U.S. National Archives
• Korean War and Japan's Recovery — Office of the Historian, U.S. Department of State
• Korean War — National Army Museum
• Korean War: How the Cold War Became a Hot War — Reha Mert, World History Encyclopedia, 2026
• Korean War — Wikipedia