For centuries before 1945, Korea had been a unified political entity. The origins of the modern division of Korea trace to the period of Japan's colonial rule over Korea (1910-1945). During World War II, the Allied leaders fighting Japan considered the question of Korea's future after Japan's surrender in the war. The leaders reached an understanding that Korea would be liberated from Japan but would be placed under an international trusteeship until the Koreans would be deemed ready for self-rule. Beyond this rather vague agreement, much about the future of Korea was left uncertain.