<P> When the Russo - Japanese War ended in 1905 Korea became a nominal protectorate of Japan, and was annexed by Japan in 1910 . The Korean king Gojong was removed . In the following decades, nationalist and radical groups emerged, mostly in exile, to struggle for independence . Divergent in their outlooks and approaches, these groups failed to unite in one national movement . The Korean Provisional Government in China failed to obtain widespread recognition . </P> <P> In November 1943, Franklin Roosevelt, Winston Churchill and Chiang Kai - shek met at the Cairo Conference to discuss what should happen to Japan's colonies, and agreed that Japan should lose all the territories it had conquered by force . In the declaration after this conference, Korea was mentioned for the first time . The three powers declared that they were, "mindful of the enslavement of the people of Korea,...determined that in due course Korea shall become free and independent ." Roosevelt floated the idea of a trusteeship over Korea, but did not obtain agreement from the other powers . Roosevelt raised the idea with Joseph Stalin at the Tehran Conference in November 1943 and the Yalta Conference in February 1945 . Stalin did not disagree, but advocated that the period of trusteeship be short . </P> <P> At the Tehran Conference and the Yalta Conference, the Soviet Union promised to join its allies in the Pacific War in two to three months after victory in Europe . On August 8, 1945, three months to the day after the end of hostilities in Europe, and two days after the atomic bomb was dropped on Hiroshima, 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 August 10, 1945 two young officers--Dean Rusk and Charles Bonesteel--were assigned to define an American occupation zone . Working on extremely short notice and completely unprepared, they used a National Geographic map to decide on the 38th parallel . They chose it because it divided the country approximately in half but would place the capital Seoul under American control . No experts on Korea were consulted . The two men were unaware that forty years before, Japan and pre-revolutionary Russia had discussed sharing Korea along the same parallel . Rusk later said that had he known, he "almost surely" would have chosen a different line . The division placed sixteen million Koreans in the American zone and nine million in the Soviet zone . 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 . </P> <P> Soviet forces began amphibious landings in Korea by August 14 and rapidly took over the north - east of the country, and on August 16 they landed at Wonsan . On August 24, the Red Army reached Pyongyang . </P>

When did korea break into north and south