The imperial occupation of Korea by Japan from 1905-1945 sowed the seeds of future division and provided an incubator for rival factions to flourish and energize. After Japan was defeated and Korea liberated in 1945, Soviet-American agreements exploited the divisions that had sprung up during the previous decades. Fueled by old resentments, nationalistic movements, and cold war politics, the Soviet-American actions drove a wedge between North and South Korea, precipitated the Korean War, and erected a lasting wall dividing a country that 50 years earlier had been united.
The seeds of division began to be sowed with the arrival of Japanese influence in the Korean peninsula. The 1876 treaty of Ganghwa between Japan and Korea was negotiated to open up trade between the two nations. However, the technically disadvantaged and militarily weaker Korea succumbed to a treaty that greatly favored the Japanese. It limited China's relatively innocuous influence, which setup Korea as a target for future imperialism. Russia, with imperialistic intentions, attempted to exert power over Korea during the 1890s. Japan and Russia, the biggest influences in Korea during this period, could not reach an agreement over the division of the spheres of influence. After negotiations broke down in 1904, Japan successfully defeated the Russians by initiating an attack on Russian ships harbored at Port Arthur (Cumings, 141). The agreement, negotiated by President Theodore Roosevelt, was little more than a U.S. trade off with Japan in which the U.S. got the Philippines and Japan was rewarded with Korea. This would be the beginning of 40 years of imperial rule by Japan and sweeping social and political changes.
After 1905 Japan enjoyed a great latitude of control over Korea. They had been successful in defeating the Chinese and the Russians and had the silent approval of both the Americans and the British (Cumings, 142). This control began to reshape Korea and in doing so began to splinter the society. The beginnings of communism in Korea had their roots in the 1920s as rifts between the left and right began to manifest. Woodrow Wilson's assurances of self-determination had not been realized in Korea. On March 1, 1919, an uprising against the Japanese, demanding independence, resulted in a months long violent revolt. The suppression of the rebellion by Japanese authority left citizens divided with many turning to communist organizations for support. The division was split along left-right lines and mirrored the policies of Wilson and Lenin. The new policy of "gradualism" had resulted in a greater freedom of speech and encouraged the formation of several nationalistic, communist, and socialist groups. Occasionally these groups would be encouraged by the Japanese as a method to, "corral, co-opt, or simply moderate independence activist on left and right" (Cumings, 156). By the end of the 1920s, the communists were the main group leading the call for independence. Communism appealed to many Koreans as Dae-sook Suh writes, "The haggard appearance of the communists suffering from torture, their stern and disciplined attitude toward the common enemy of all Koreans, had a far reaching effect on the people" (qtd. in Cumings, 158). The geographical proximity of China favored the communists in the north and the resistance groups that this created would later become