Korea had been ruled by Japan from 1910 until the end of World War II. In 1948 the USSR and United States partitioned Korea into two countries, North Korea and South Korea. At the time, U>S> efforts were focused on Europe as a potential powderkeg.
On June 25, 1950. some 75,000 North Korean troops spilled over the 38th parallel dividing the two countries. In 1951, China intervened on behalf of the North Koreans and at times the United Nations forces seemed on the brink of losing.