The Cambodian campaign was a series of military operations conducted in eastern Cambodia in mid-1970 by South Vietnam and the United States as an expansion of the Vietnam War and the Cambodian Civil War. Thirteen operations were conducted by the Army of the Republic of Vietnam (ARVN) between April 29 and July 22 and by U.S. forces between May 1 and June 30, 1970.

South Vietnam, officially the Republic of Vietnam, was a country in Southeast Asia that existed from 1955 to 1975, the period when the capitalist southern portion of Vietnam was a member of the Western Bloc during part of the Cold War after the 1954 division of Vietnam. It first received international recognition in 1949 as the State of Vietnam within the French Union, with its capital at Saigon, before becoming a republic in 1955. South Vietnam was bordered by North Vietnam to the north, Laos to the northwest, Cambodia to the southwest, and Thailand across the Gulf of Thailand to the southwest. Its sovereignty was recognized by the United States and 87 other nations, though it failed to gain admission into the United Nations as a result of a Soviet veto in 1957. It was succeeded by the Republic of South Vietnam in 1975. In 1976, the Republic of South Vietnam and North Vietnam merged to form the Socialist Republic of Vietnam.