Korean reunification selected the 38th parallel as a dividing line. Japanese troops to the North of this line were to surrender to the Soviet Union and troops to the South of this line would surrender to the United States. This was not originally intended to result in a long-lasting partition, but Cold War politics resulted in the establishment of two separate governments in the two zones in 1948 and rising tensions prevented cooperation. The desire of many Koreans for a peaceful unification was dashed when the Korean War broke out in 1950. In June 1950, troops from North Korea invaded South Korea.
Soviet Union in the Korean War the United States and its allies elsewhere, which could have led to a nuclear war. By officially denying its participation, the Soviets prevented the Korean War from escalating. Participation on the North Korean side was also contrary to the UN Security Council Resolution 84 by which the Soviet Union was technically bound. Along with several "Eastern Block" countries (notably Czechoslovakia), the Soviet Union sent over 20 doctors to Korea to aid Communist forces there, similar to Indian, Italian, Norwegian, Danish and Swedish medical detachments in Southern Korea who did not have military force engaged, but merely offered humanitarian support instead.