The People's Volunteer Army ambushed the South Korean II Corps at the Battle of Onjong, and elsewhere engaged the 1st Infantry Division at the Battle of Unsan, marking China's entry into the Korean War.

The People's Volunteer Army (PVA), officially the Chinese People's Volunteers (CPV), was the designation for the Chinese communist contingent of armed expeditionary forces deployed by the People's Republic of China during the Korean War. Although all units in the PVA were actually transferred from the People's Liberation Army (PLA) under the orders of Chairman Mao Zedong, the PVA was separately constituted in order to prevent an official war with the United States. The PVA entered Korea on 19 October 1950 and completely withdrew by October 1958. The nominal commander and political commissar of the PVA was Peng Dehuai before the ceasefire agreement in 1953, although both Chen Geng and Deng Hua served as the acting commander and commissar after April 1952 following Peng's illness. The initial units in the PVA included 38th, 39th, 40th, 42nd, 50th, 66th Corps; totalling 250,000 men. About 3 million Chinese civilian and military personnel had served in Korea throughout the war.