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 The U.S. 101st Airborne Division left South Vietnam, the last U.S. ground combat division to be withdrawn from South Vietnam.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
1972 in the Vietnam War mines off the coast of North Vietnam to prevent ship travel to and from the country. Operation Linebacker II began. Better known as the "Christmas bombings", 129 B-52s and smaller tactical aircraft struck at targets in North Vietnam, including around the city of Hanoi. North Vietnam shot down three B-52s. Military adviser Alexander Haig met with President Thieu in Saigon to deliver a letter from President Nixon. Nixon said it was his "irrevocable intention" to achieve a peace agreement with North Vietnam, preferably with the cooperation of South Vietnam, "but, if necessary, alone." He pledged continue military support to South