Japan, however, was very worried about the possibility Russia expanding into Korea during the nineteenth-century. And in the early twentieth century, Japan was particularly concerned about the future of Korea because, as a colony, they used it as an agricultural breadbasket to provide their growing urban-industrial classes with rice. While Japan's desire for Korea grew, its options seemed to be limited by the fact that in the face of Japanese aggression, Korea could appeal to the Russians, who controlled neighboring Manchuria, for assistance. In large part, the Japanese fought the Sino-Russian war as an effort to eliminate the Russians as a rival for control of Korea. Incidentally, though Teddy Roosevelt's mediation of the Sino-Russian War in 1905 may have won him a Nobel Peace Prize, it also won the US the long-term hatred of the Japanese.
Because of Japanese domination of Korea in the first half of the twentieth century that culminated with Japan's insulting treatment of Korea during World War II, the Koreans developed a deep hatred of their Japanese overlords, and developed a strong nationalism. Koreans tended to look favorably towards Russia, which had been Japan's recent enemy for influence in the region. Indeed, it was no surprise that many Koreans borrowed from developments in Russia and became Communists themselves. The fact that the most powerful businessmen in Korea were Japanese, while the workers were Korean, was a further reason many Koreans were especially receptive to the Marxist message urging workers to unite and take power. By the end of World War II, much of the Korean population was genuinely pro-Soviet. Therefore, in terms of the Korean War, it is important to recognize that while the Soviet Union had a long history of being interested in Korea's fate, American policymakers saw the country as only an abstract of pawn of symbolic importance in the Cold War.