According to Korean mythology in 2333 BCE, the Gojoseon Kingdom was established by the god-king Dangun. Following the unification of the Three Kingdoms of Korea under Unified Silla in 668 AD, Korea was subsequently ruled by the Goryeo dynasty (918–1392) and the Joseon dynasty (1392–1897). In 1897, King Gojong proclaimed the Korean Empire, which was annexed by the Empire of Japan in 1910.[18]

From 1910 to the end of World War II in 1945, Korea was under Japanese rule. Most Koreans were peasants engaged in subsistence farming.[19] In the 1930s, Japan developed mines, hydro-electric dams, steel mills, and manufacturing plants in northern Korea and neighboring Manchuria.[20] The Korean industrial working class expanded rapidly, and many Koreans went to work in Manchuria.[21] As a result, 65% of Korea's heavy industry was located in the north, but, due to the rugged terrain, only 37% of its agriculture.[22]

Northern Korea had little exposure to modern, Western ideas.[23] One partial exception was the penetration of religion. Since the arrival of missionaries in the late nineteenth century, the northwest of Korea, and Pyongyang in particular, had been a stronghold of Christianity.[24] As a result, Pyongyang was called the "Jerusalem of the East".[25]

A Korean guerrilla movement emerged in the mountainous interior and in Manchuria, harassing the Japanese imperial authorities. One of the most prominent guerrilla leaders was the Communist Kim Il Sung.[26]