https://www.warhistoryonline.com/history/first-united-states-military-involvement-korea-1871.html
The First U.S. Military Involvement in Korea: The Korean Expedition (1871)
Jun 14, 2017 - While some think the United States was not involved with Korea until the Korean War, they actually were in the region during the Korean Expedition.
u s militarythe firstin koreakorean expedition