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.
North Korea–South Korea relations
The US government took the issue to the United Nations, which led to the formation of the United Nations Temporary Commission on Korea (UNTCOK) in 1947. The Soviet Union opposed this move and refused to allow UNTCOK to operate in the North. UNTCOK organised a general election in the South, which was held on May 10, 1948. The Republic of Korea was established with Syngman Rhee as President, and formally replaced the US military occupation on August 15. In North Korea, the Democratic People's Republic of Korea was declared on September 9, with Kim Il-sung, as prime minister. Soviet occupation forces left the North on December 10, 1948. US forces left the South the following year, though the US Korean Military Advisory Group remained to train the Republic of Korea Army.