United States Army Military Government in Korea

The Japanese flag in front of the Japanese Government-General of Korea building in Seoul is replaced with the U.S. flag.

The United States Army Military Government in Korea (USAMGIK) was the United States' occupying authority in the southern part of Korea from September 8, 1945 until August 15, 1948.

Prior to the arrival of U.S. forces in Korea, Koreans had established various organizations for self-government, such as numerous People's Committees throughout the country as well as declaring the short-lived People's Republic of Korea (PRK). These forms of self-government had grown out of Korea's independence struggle, and were able to come out into the open and further expand after imperial Japan's defeat. However, USAMGIK did not recognize the authority of the PRK nor the People's Committees and proceeded to outlaw and dismantle them, and created new local councils under conservative control as well as rehired officers from the Japanese colonial era.

Richard D. Robinson, a historian who at the time of USAMGIK's occupation was the chief of the Public Opinion Section of the Department of Information of the USAMGIK, has been quoted describing the occupation as "incredibly bungled by an incompetent and corrupt administration" and has further been quoted describing the situation as follows:

It was safe to say that for the most part the local People's Committees in these early days were of the genuine grassroots democratic variety and represented a spontaneous urge of the people to govern themselves. [...] They resented orders from the Military Government to turn the administration of local government over to American Army officers and their appointed Korean counterparts, many of whom were considered to be Japanese collaborators. It seemed like a reversion to what had gone before. Bloodshed ensued in many communities as local People's Committees defied the Military Government and refused to abandon government offices. Koreans and Americans met in pitched battles, and not a few Koreans met violent death in the struggle.

Ahn Hak-sop, a former officer in the Korean People's Army who was captured in 1952 and endured decades of torture as a political prisoner in south Korea, spoke about the USAMGIK's occupation in a 2019 interview with Liberation School:

In September of 1945, Koreans went out to greet the US Army, but the US Army shot at them. After the Moscow Committee, the US Army said explicitly that they were there to block the Soviet Union. But in 1948, the Soviet Union withdrew all of their troops. But the US Army didn’t withdraw. In almost every town, there was a People’s Committee for self-rule, but the US Army crushed the People’s Committees with tanks and soldiers.

The "Jeju 4•3 Incident Investigation Report" published in 2003 by south Korea's government assigns responsibility for the Jeju massacre not only to dictator Syngman Rhee but also to the USAMGIK authorities.