Given thirty minutes to do so...

[koganbot]

In the days just before Koreans heard the voice of Emperor Hirohito for the first time, broadcasting Japan's surrender and Korea's liberation on August 15, 1945, John J. McCloy of the State-War-Navy Coordinating Committee (SWNCC) directed two young colonels, Dean Rusk and Charles H. Bonesteel, to withdraw to an adjoining room and find a place to divide Korea. It was around midnight on August 10-11, the atomic bombs had been dropped, the Soviet Red Army had entered the Pacific War, and American planners were rushing to arrange the Japanese surrender throughout the region. Given thirty minutes to do so, Rusk and Bonesteel looked at a map and chose the thirty-eighth parallel because "it would place the capital city in the American zone"; although the line was "further north than could be realistically reached... in the event of Soviet disagreement," the Soviets made no objections-which "somewhat surprised" Rusk.
--Bruce Cumings, Korea's Place In The Sun, Updated Edition, pp 186-187.