There was a lot of unfinished business on the Korean peninsula in the 1940's. It had been ruled by the Empire of Japan from 1910 until the end of World War II, when it was divided by American administrators along the 38th parallel, with U.S. military forces occupying the southern half and Soviet military forces occupying the northern half. The failure to hold free elections throughout the Korean Peninsula in 1948 deepened the division between the two sides; the North established a communist government, while the South established a right-wing government under Syngman Rhee. Cross-border skirmishes and raids at the 38th Parallel persisted until North Korean forces invaded South Korea on 25 June 1950. The USSR boycotted the United Nations Security Council because the Republic of China, now operating from Taiwan, was chosen to represent China in the UN. Without the Soviet veto, the Security Council resolution authorizing military intervention in Korea. The vast majority of “international” troops were American.
When the war broke out, Donald MacDonald, who was stationed in Korea at the time and discusses, in an interview with Stu Kennedy in 1990, what it was like coming into Korea in June 1948, the relationship between the United States and the Rhee government and the phone call early in the morning of June 25th that informed MacDonald of the unfolding “little” emergency.