At the Cairo conference of 1943 the Allies agreed that Korea (which had been a Japanese colony and under the country's occupation since 1910) would be freed of Japanese domination. Russian troops advanced rapidly through northern Korea and in August 1945 were victorious over Japan. The American President, Harry Truman, declared the 38th parallel of latitude as the line of separation between American and Soviet influence in Korea.
In the north the Russians set up a communist state - the <<Democratic People's Republic of Korea (DPRK)>> under Kim II Sung. In the south the Americans established the Republic of Korea under Syngman Rhee. Although Russian and American troops withdrew from Korea by mid-1949, considerable tension remained between the two new states.
The <<North Korean Peoples' Army>> invaded South Korea in June 1950 and made rapid progress, occupying Seoul within days. The US government regarded the invasion as a threat to its national interests and, with British support, appealed to the United Nations (UN) Security Council. North Korea was declared the aggressor. At this time the USSR was boycotting the Security Council of the UN and Western Allies commanded a majority on the Council. In June a largely American UN force arrived in Korea and the British government deployed the Far East Fleet in support.
Within the Labour Party support for the war was controversial as it was not an immediate threat to Britain's interests. In contrast, the American leadership cast the war as part of a wider struggle against communism in the east and deployed its Seventh Fleet to prevent a possible Chinese invasion of Formosa (Taiwan). Although Britain had already imposed economic sanctions against North Korea, the US requested that Britain extend sanctions against China.
The Labour government was anxious 'not to offer an affront' to communist China, fearing a possible threat to Hong Kong, and decided against imposing sanctions. In that period Britain was also committed to defending the government in Malaya against an insurgency and had promised the French government assistance in Vietnam. Given the general view that Britain should not overstretch her already scarce resources in the East, on 6 July Cabinet decided against sending further military forces to Korea. The decision was reversed on 25 July, however, when Foreign Office concerns about the affront to the US and fears about Britain's position in the Cold War overcame Cabinet doubts.
On 29 August 1950 the first British ground force, 27 Brigade, arrived in Korea to defend the Pusan perimeter. The British troops of 27 Brigade were joined by 3rd Battalion and the Royal Australian Regiment - and the Brigade was renamed 27 Commonwealth Brigade. Meanwhile, Royal Navy ships were engaged in the counter-offensive that started with The Inchon landing, and the amphibious raids mounted by the Royal Marine Commandoes.
On 16 September in the south 27 Commonwealth Brigade were involved in the breakout from the Pusan perimeter, and by the end of October they were advancing through North Korea as the UN forces surged northwards. In November 1950, at the same time that the second and much stronger British force arrived, the Chinese launched an attack on UN forces moving up along the Yalu River to the border of North Korea and China.
In the west the Americans fell back towards 27 Commonwealth Brigade while UN units within the 8th Army fell back to the Chongchon River. Quickly defeated by Chinese forces, the 8th Army was forced to retreat and by 5 December was back on the 38th parallel of latitude. By January 1951 27 Commonwealth Brigade and 29 Brigade were defending the approaches to and from Seoul. After inflicting a sharp defeat on the advancing Chinese, both brigades were withdrawn and Seoul was abandoned. After months of heavy fighting UN forces checked the Chinese advance, pushing them back beyond the Han River to recapture Seoul.