The Korean War

korean war

More than 36,500 US soldiers died in the Korean War

A new front in the Cold War opened in 1949, after China was seized by communists and war erupted in Korea. The Korean peninsula – bordering Manchuria (China) to the north and separated from Japan by a narrow strait – had long been coveted by its neighbours, particularly the Japanese. Japan went to war with China (1894-95) and Russia (1904-5) over control of Korea, before finally annexing it in 1910. The Japanese defeat in 1945 raised the question of who would rule post-war Korea. Several local groups within Korea vied for control – however the leaders of America and Soviet Russia had already agreed to a joint occupation of the peninsula. In August 1945, days after the bombing of Hiroshima, a joint agreement divided the Korean peninsula into two at the 38th parallel (the line of latitude 38 degrees north of the equator). The Soviet Red Army would occupy the north, while the Americans would occupy the south. The agreement was intended to be temporary but included no clear plan or timeline for Korean self-government or unification.

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Soldiers of the US 7th division arrive in Incheon, Korea in September 1945

As in divided post-war Germany, the political development in Korea’s northern and southern zones was strongly influenced by the occupying powers. In South Korea, the Americans resisted local independence movements which they considered too left-wing. Washington instead gave local government to Syngman Rhee, a hardline anti-communist. Rhee began targeting suspected communists with violent purges that claimed in excess of 50,000 lives. Meanwhile in the north, the Soviets formed a provisional government with Kim Il-Sung as ruler. Kim initiated a program of land reform and redistribution that was popular with local peasants – but like Rhee, Kim also initiated political violence and murderous purges to eliminate his political opposition. Despite United Nations involvement, it soon became apparent that no unification of Korea would be possible. As a result, the two zones became independent nation-states in 1948. Tensions between North and South Korea increased, as their leaders engaged in aggressive political rhetoric. They also fortified the 38th parallel border and increased military garrisons in the area, leading to cross-border shootings and skirmishes. In June 1950, one of these incidents sparked a full-scale invasion of South Korea by the North Korean People’s Army (KPA).

The North invades

Within days of the invasion, US president Harry Truman ordered American troops into South Korea to resist the communists. This decision was difficult for Truman, who thought American involvement might provoke a war with communist China – or worse still, the USSR. But intelligence provided to the White House claimed the North Koreans had invaded with authorisation from Moscow, and most of Truman’s advisors supported “drawing a line” against communist expansion in Asia. Truman’s mobilisation order drew a hostile response from the Soviet Union. Moscow condemned American interference, boycotted meetings of the United Nations Security Council and pledged to support the North Koreans, though without direct military involvement. Pravda, the state-controlled newspaper in Moscow, described US involvement thus:

“The events in Korea … reveal with all clarity that the imperialist warmongers will not stop half-way in pursuit of their goal. As is known, on June 25th the provocative actions of troops of the puppet government of South Korea, directed against the Korean People’s Democratic Republic, unleashed military operations in the territory of Korea. In reply to this, security detachments and troops of the Korean People’s Democratic Republic undertook active measures and went on the counter-offensive, transferring military operations to the territory south of the 38th parallel. [President] Truman’s statement and actions, unprecedented in the international relations of the post-war period, constitute further evidence that the American ruling circles no longer confine themselves to the preparation of aggression, but have gone over to direct acts of aggression … The American Government is grossly trampling on the United Nations Charter, acting as though the United Nations organisation does not exist at all.”

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General Douglas Macarthur, who led US forces in Korea until 1951

On the ground in Korea, the KPA’s vast numerical advantage (the North had more than 230,000 soldiers, the South less than 100,000) allowed it to surge quickly into South Korean territory. By September 1950, North Korean forces would occupy 90 percent of the Korean peninsula; while the South Koreans and Americans were confined to a small region around the coastal city of Pusan. But help was coming, in the guise of a 17-nation coalition force, backed by a United Nations resolution. Among the nations who sent troops to resist communist aggression in South Korea were Great Britain, France, Canada, Australia, New Zealand, South Africa, Turkey, Thailand and Colombia. These troops began to trickle into South Korea in July and August. By September, US general Douglas MacArthur had enough men at his disposal to launch a counter-offensive against the coastal city of Inchon, not far from Seoul. By November, UN forces had pushed the KPA back to within a few miles of the Chinese border.


China intervenes

“Since the early 1980s much of the debate over the Korean War has focused on the argument that the conflict was a civil war, mistakenly viewed by the Western allies as a manifestation of the struggle between the United States and the Soviet Union. On most counts, the Russian documentary sources sharply contradict this civil war thesis. They reveal that the outbreak of full-scale fighting along the 38th parallel … was not simply an escalation of border skirmishes… but was instead a conventional offensive campaign prepared by North Korea and the Soviet Union over several months. Most important, the decision to undertake the campaign to seize control over southern Korea was made by Josef Stalin, not by the North Korean leadership.”
Kathryn Weathersby, historian
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A map showing the Chinese advance into Korea in 1950-51

For the next four months, as KPA and UN forces wrestled for territory, a sideshow conflict erupted between Truman and General Douglas MacArthur, his military commander in Korea. MacArthur’s plan for victory involved pursuing North Korean troops back into Chinese territory, bombing air bases in China and, if necessary, using tactical nuclear weapons. Truman, eager to avoid war with China and certainly averse to using nuclear weapons again, refused MacArthur’s proposal. This prompted MacArthur to make a number of inflammatory statements to the media, containing implied criticisms of how the White House was handling the war. In April 1951 a fed-up Truman sacked MacArthur. Given that MacArthur was a hero of World War II, the Pacific commander whose leadership defeated the Japanese, removing him was a difficult decision for Truman. But MacArthur – who had conducted the war from the safety of Tokyo – had certainly exceeded his authority.

Meanwhile, a more dramatic situation was unfolding on the battlefield. With UN forces on its doorstep, China decided to intervene in late 1950, sending almost 200,000 troops into North Korea. The US and UN forces were again forced to retreat to South Korean territory. Between early 1951 and mid-1953, the Korean War fell into stalemate, with neither belligerent able to capture or reclaim significant territory. There were several major battles and a large number of casualties during this period, the majority incurred by the North Koreans and Chinese. The to-and-fro continued until July 1953 when a ceasefire was signed in Panmunjom – ironically, with opposing forces fighting just a few miles from the 38th parallel. After three years of war and between 2.5 and 3 million deaths, the two Koreas remained separated by a border, roughly in the same place as 1949. No treaty to end the Korean War was ever signed, so North and South technically remain at war but in a state of ceasefire. More than a half-century since the war was halted, the De-Militarised Zone (DMZ) that separates North and South Korea is guarded by one of the heaviest military garrisons on any national border. More than 500 South Korean and 50 US soldiers have been killed in or near the DMZ since 1953.



1. Korea is a peninsula nation in south-east Asia that was occupied by the Japanese during World War II.
2. In 1945 Korea was jointly occupied by Soviet troops north of the 38th parallel, and the Allies in the south.
3. These occupation zones developed as separate nations, led by Kim Il-Sung (North) and Syngman Rhee (South).
4. In 1950 North Korea invaded the South, prompting a response from the US and a UN-backed coalition force.
5. The Chinese later became involved in the Korean War, which lasted for three years, caused around three million deaths and produced no significant change in the geopolitics of the region.

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This page was written by Jennifer Llewellyn, Jim Southey and Steve Thompson. To reference this page, use the following citation:
J. Llewellyn et al, “The Korean War”, Alpha History, accessed [today’s date],