Soviet and U.S. Armed forces entered into the Korean peninsula in August and September, 1945, respectively. That was the beginning of the Russo-American confrontation. From that point on to Korean War in 1950, the United States and Soviet Union initiated the Cold War in Asia for the purpose of enlarging their territories into their sphere. At the same time, the United States and Soviet Union were engaged in strategic initiatives and intelligence maneuvers on the Korean peninsula. This confrontational situation was resulted into the hot Korean War.
After consolidating their Communist system of government in the North, soviet Union exerted their efforts to enlarge their sphere of influence into South Korea by infiltrating and directing insurgency into the South.
The United States XXIVth Corps also sparred no time to Mobilize their Humit and Comint abilities to Collect valuable information and intelligence on the part of Russians and North Korea, and they had certain success in that respect. The withdrawn American forces from South Korea in June 1949 did not go too far through Pacific, but most of them were relocated in Japan proper and Okinawa. As soon as the Korea War was broken out, they were the first ones to come to the aid of Korea, at the prompt directions by the American leadership and the Far East Command in Japan in order to repel the North Korean invasion forces and to unify the Korean peninsula at the close of war.
Nonetheless, the American intelligence made fatal mistakes in their estimates on the Chinese intervention, even though they were provided with plenty of valuable information and intelligence. They say, all faults came about from MacArthur's habitual tendency of not compromising with his intelligence staff.