10 August 1945
Korea Divided along 38th Parallel
On August 8, in accordance with promises made at the Yalta Conference, the Soviet Union declared war on Japan. Soviet forces immediately swept through Japanese-held Manchuria and into Korea, which had been a Japanese possession since 1910. At the same time, President Truman—by now concerned that the Soviets might attempt to dominate all East Asia—ordered the landing of U.S. forces on the southern tip of the Korean peninsula.

Two days later, with Japan’s surrender imminent, the United States and the Soviet Union concluded an agreement by which Korea would be divided along the 38th parallel. All Japanese forces north of that line would surrender to Soviet troops, while those to the south would surrender to the Americans. Temporarily, at least, northern Korea would be occupied and administered by the Soviet Union, while U.S. forces would dominate in the south.

- Occupation and Surrender of Southern Korea, 8-9 September 1945