US Lieutenant General John R. Hodge was appointed as military governor. He directly controlled South Korea as head of the United States Army Military Government in Korea (USAMGIK 1945–48). In December 1945, Korea was administered by a US-Soviet Union Joint Commission, as agreed at the Moscow Conference, with the aim of granting independence after a five-year trusteeship. The idea was not popular among Koreans and riots broke out. To contain them, the USAMGIK banned strikes on 8 December 1945 and outlawed the PRK Revolutionary Government and the PRK People's Committees on 12 December 1945. Following further large-scale civilian unrest, the USAMGIK declared martial law.

Citing the inability of the Joint Commission to make progress, the US government decided to hold an election under United Nations auspices with the aim of creating an independent Korea. The Soviet authorities and the Korean Communists refused to co-operate on the grounds it would not be fair, and many South Korean politicians boycotted it. A general election was held in the South on 10 May 1948. North Korea held parliamentary elections three months later on 25 August.

The resultant South Korean government promulgated a national political constitution on 17 July 1948, and elected Syngman Rhee as President on 20 July 1948. This election is generally considered to have been manipulated by the Rhee regime. The Republic of Korea (South Korea) was established on 15 August 1948. In the Soviet Korean Zone of Occupation, the Soviet Union agreed to the establishment of a communist government led by Kim Il-sung. The Soviet Union withdrew its forces from Korea in 1948, and US troops withdrew in 1949.