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 The U.S. 101st Airborne Division left South Vietnam, the last U.S. ground combat division to be withdrawn from South Vietnam.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
1973 in the Vietnam War Nixon promised continued economic aid to South Vietnam, dependent upon U.S. congressional approval, and Thieu pledged to never ask the United States to reintroduce American troops into South Vietnam. The US and North Vietnam issued a joint communique calling on all parties to observe the 28 January ceasefire agreement with effect from 15 June. The Case–Church Amendment approved by the U.S. Congress and signed into law prohibited further U.S. military activity in Vietnam, Laos and Cambodia after 15 August 1973. This ended direct U.S. military involvement in the Vietnam War, although the U.S. continued to provide military equipment and economic