1972 in the Vietnam War the number of air raids against North Vietnam during all of 1971. Prime Minister Lon Nol declared President of Cambodia. Unlike the former Cambodian leader, Norodom Sihanouk, Lon Nol was a U.S. ally. The U.S. 101st Airborne Division left South Vietnam, the last U.S. ground combat division to be withdrawn from South Vietnam. The Khmer Rouge bombarded with artillery Phnom Penh, the capital city of Cambodia, killing more than 100 civilians. This was the heaviest attack on Phnom Penh since the Cambodian Civil War began in 1970. The United States boycotted peace negotiations in Paris with the North Vietnamese, citing
1955 in the Vietnam War former colonial ties to France. The United States closed its embassy in Hanoi, thus ending formal diplomatic relations with North Vietnam. The U.S. would not restore diplomatic relations until 1998. China informed North Vietnam that all members of the China Military Advisory Group, which had been in Vietnam since July 1950, would return to China. This action by China illustrated the Chinese view that the most important task of North Vietnam was to consolidate its rule rather than attempt to force reunification with South Vietnam. 1955 in the Vietnam War In 1955, the Prime Minister of South Vietnam Ngô Đình