North Korea
Japan tried to suppress Korean traditions and culture and ran the economy primarily for its own benefit. Korean resistance groups known as Dongnipgun (Liberation Army) operated along the Sino-Korean border, fighting guerrilla warfare against Japanese forces. Some of them took part in allied action in China and parts of South East Asia. One of the guerrilla leaders was the communist Kim Il-sung, who later became the first leader of North Korea.
South Korea
Despite the initial plan of a unified Korea in the 1943 Cairo Declaration, escalating Cold War antagonism between the Soviet Union and the United States eventually led to the establishment of separate governments, each with its own ideology, leading to the division of Korea into two political entities in 1948: North Korea and South Korea. In the South, Syngman Rhee, an opponent of communism, who had been backed and appointed by the United States as head of the provisional government, won the first presidential elections of the newly declared Republic of Korea in May. In the North, however, a former anti-Japanese guerrilla and communist activist, Kim Il-sung was appointed premier of the Democratic People's Republic of Korea in September.