The aim of Japanese colonial policy was to incorporate Korea into an expanding empire as a subordinated supplier of raw materials and labour whose inhabitants were to be stripped of national rights and aspirations. The intent was to eradicate Korean national identity and to force Koreans to assume loyalty to the Japanese state and the Emperor. The politics of colonialism brought annexation and militarised occupation enforced by a coercive police apparatus. The economics of colonialism brought rapid industrialisation accompanied by mass migration that provided labour for the huge new manufacturing plants established by Japanese business in the north-east of the peninsula, in what is today the Democratic People's Republic of Korea (DPRK). The social dislocations brought about by colonial policy combined with the repression through which policy was enforced engendered the radicalisation of the population.

The denial of Korean independence and national identity and the increasingly militarised occupation, combined with the absence of outlets for moderate opposition to Japanese policies, narrowed the political options open to Korean nationalist leaders. Peaceful demonstrations failed to achieve political change, nationalist leaders were often forced into exile and some pursued guerrilla warfare from bases across the contiguous Chinese border. The Japanese military ferociously hunted down and killed members of armed opposition groups, and Kim Il Sung, based first in Manchuria and then in the Soviet far east, was one of the very few survivors of Japanese retribution.

Soviet troops, representing the Allied powers, entered and occupied northern Korea in August 1945. The thirty-eighth parallel almost immediately hardened into a territorial and ideological border between two political quasi state-like bodies in the northern and southern parts of the peninsula. The Soviet Union did not intend to remain in Korea but did intend to leave behind a regime friendly to the communist superpower. Soviet authorities promoted Kim Il Sung as de facto political Leader of the north and, in 1948, supported Kim Il Sung as the first Leader of the newly established sovereign state of the Democratic People's Republic of Korea (DPRK).