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.
Workers' Party of Korea
Kim Il-sung was not the most ardent supporter of a military reunification of Korea; that role was played by the South Korean communists, headed by Pak Hon-yong. After several meetings with Joseph Stalin (the leader of the Soviet Union), the North Koreans invaded South Korea on 25 June 1950—this began the Korean War. With American intervention in the war the DPRK nearly collapsed, but it was saved by Chinese intervention in the conflict. The war had the effect of weakening Soviet influence over Kim Il-sung and the WPK. Around this time, the main fault lines in early WPK politics were created. Four factions formed: domestic (a group of WPK cadres who had remained in Korea during Japanese rule), Soviet Koreans (Koreans sent from the Soviet Union), Yanan (Koreans from China) and guerrillas (Kim Il-sung's personal faction). However, Kim would be unable to further strengthen his position until the end of the war.