thumb|left|Welcome celebration for the Red Army in Pyongyang on 14 October 1945 At the Tehran Conference in November 1943 and the Yalta Conference in February 1945, the Soviet Union promised to join its allies in the Pacific War within three months of victory in Europe. On 8 August 1945, after three months to the day, the Soviet Union declared war on Japan. Soviet troops advanced rapidly, and the US government became anxious that they would occupy the whole of Korea. On 10 August, the US government decided to propose the 38th parallel as the dividing line between a Soviet occupation zone in the north and a US occupation zone in the south. The parallel was chosen as it would place the capital, Seoul, under American control. To the surprise of the Americans, the Soviet Union immediately accepted the division. The agreement was incorporated into General Order No. 1 (approved on 17 August 1945) for the surrender of Japan. The division placed sixteen million Koreans in the American zone and nine million in the Soviet zone.
thumb|left|Welcome celebration for the Red Army in Pyongyang on 14 October 1945 At the Tehran Conference in November 1943 and the Yalta Conference in February 1945, the Soviet Union promised to join its allies in the Pacific War within three months of victory in Europe. On 8 August 1945, after three months to the day, the Soviet Union declared war on Japan Soviet troops advanced rapidly, and the US government became anxious that they would occupy the whole of Korea. On 10 August, the US government decided to propose the 38th parallel as the dividing line between a Soviet occupation zone in the north and a US occupation zone in the south. The parallel was chosen as it would place the capital, Seoul, under American control. To the surprise of the Americans, the Soviet Union immediately accepted the division. The agreement was incorporated into General Order No. 1 (approved on 17 August 1945) for the surrender of Japan. The division placed sixteen million Koreans in the American zone and nine million in the Soviet zone.