The Korean War was caused by the conditions holding since the end of World War Two. Korea had been split in half along the 38th parallel, with the USSR holding the north and the USA holding the south. As each sponsor state helped its occupied area to set up their own government, the two Koreas moved in increasingly different directions. Although negotiations for reunification continued almost up to the outbreak of war, tensions rose throughout the period especially from 1948 onwards.
On June 25th, 1950, North Korean forces poured over the border into South Korea, and the war began. The South Koreans were swiftly joined by a US-led coalition backed by the United Nations (the USSR was boycotting the UN Security Council at this point, and was thus unable to veto this action). The would last into 1953, costing hundreds of thousands of lives, until a ceasfire was negotiated, with the border still set roughly at the 38th parallel with little change to its pre-war location.
On June 25, 1950, North Korean forces poured over the border separating the North and South parts of the peninsula, invading South Korea. This was considered a threat by the United States for two reasons: first, because the North Korean regime was Communist, and the Domino Theory was still widely believed; and second, because if South Korea fell, it would threaten American and allied forces in Japan.
Two days later, America announced that it would come to the aid of South Korea. Aside from the desire to oppose Communism, the Truman administration was keenly aware of the failures of appeasement at the start of World War Two, and did not wish to repeat this mistake.
In the end, the Korean War would last a little more than three years, cost nearly 4 million lives in total, and set the precedent for the Vietnam War – all for some very minor changes in the border between the two states.
The 19th, 22nd and 92nd Bombardment Groups were reassigned from Strategic Air Commaned bases in the United States to new bases in South Korea and placed under the overall command of the Far East Air Force of the United States after the North Korean aerial attacks of June 25, 1950. Mostly flying B-29 Superfortresses, these three units were later reinforced by elements of other bombing groups, and defended on sorties by a range of fighter aircraft.
Over the course of the war, B-29s flew 20,000 sorties and dropped 200,000 tonnes (180,000 tons) of bombs. B-29 gunners are credited with shooting down 27 enemy aircraft during the conflict.