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 precarious relations between both sides, while also offering possible advantages. As American and UN soldiers were already deployed in the war on the South Korean side, it was virtually assured that Soviet forces could not engage in open and direct hostilities against the South without provoking conflicts with other UN countries. Instead, the Soviet Union was compelled to conceal its participation in the conflict (at least to the extent where Soviet involvement could still be plausibly denied by the Soviet government) so as to minimize the risk of escalating the "Cold War" into a "Hot War" with NATO and