From 1905 Korea was a state of Japan and in 1910 it was officially occupied.
The Korean War began in the closing phases of World War II when Australian communities were still coming to terms with the devastation, which that conflict had caused, and the millions it had killed as well as housing shortages and rationing of goods such as tea. Japan had control of the Korean peninsula but when Japan collapsed at the End of World War II it was entrusted to Allies, and the United Sates and the Soviet Union (Russia) divided responsibility for the country between them at the 38th parallel. Over the course of the next few years, the Soviet Union fostered a strong communist regime in the North, whilst the US supported the government in the South. By mid 1950 there was tension building between the two zones, it had gotten to such a point where hostile armies were building up along the border. On 25th June, 1950, a North Korean army finally crossed into the Southern zone and headed towards the capital Seoul. The city fell in less than a week, and North Korean forces continued their southward drive towards the strategically important port of Pusan.
After two days the US offered sea and air support to South Korea, and the United Nations Security Council asked all it's members to assist in repelling the North Korean attack. 21 nations provided troops, ships, aircraft and medical teams. Australia's contribution included 77 Squadron of the RAAF and the 3rd Battalion, Royal Australian Regiment (3 RAR), both of which were stationed in Japan at the time as part of the British Commonwealth Occupation Force. .
After 28th of September when 3 RAR arrived in Pusan, the North Korean advance had been stopped and their army was in full retreat. The Chinese government warned the supreme commander of the UN forces, General Douglas Macarthur, that the Chinese government that it would not countenance any UN troops crossing the border.