American Military History, Volume 2 by Richard W. Stewart

The North Korean invasion of South Korea on June 25, 1950, in a narrow sense was only an escalation of a continuing civil war among Koreans that began with Japan's defeat in 1945. In a larger sense, the invasion marked the eruption of the Cold War between the United States and the USSR into open hostilities because each of the Great Powers backed one of the competing Korean governments. The war that followed would devastate Korea, lead to a large expansion of the U.S. armed forces and America's military presence around the world, and frustrate many on both sides by ending in an armistice that left the peninsula still divided.

The Great Powers' connection to Korea dated back to the decision in August 1945 by the United States and the USSR to dismantle the Japanese colonial system there by dividing the peninsula into two oc- cupation zones. In December 1945 the United States and the USSR agreed to form a joint commission from among American and Soviet personnel in Korea that would recommend, after consultation with various Korean groups, the form of a government for Korea. Almost all Koreans in 1945 desired an independent Korea, but there were many competing visions of how to organize a new government.