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 The U.S. 101st Airborne Division left South Vietnam, the last U.S. ground combat division to be withdrawn from South Vietnam.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
1962 in the Vietnam War military involvement in South Vietnam, provided that the government did not include President Diệm. That same month, North Vietnamese official Lê Duẩn instructed the leadership of the Viet Cong to avoid escalating the war by attacking cities as that might cause the United States to intervene in the war. The National Liberation Front in South Vietnam proposed to end the war in South Vietnam with a ceasefire, the withdrawal of American soldiers, and the creation of a coalition government of all factions pending elections. South Vietnam would become a neutral country, as were Cambodia and Laos, guaranteed by international treaty.