Vietnam ground combat operations in 1965, and at their peak they numbered more than 500,000. The US also engaged in a sustained aerial bombing campaign. Meanwhile, China and the Soviet Union provided North Vietnam with significant material aid and 15,000 combat advisers. Communist forces supplying the Việt Cộng carried supplies along the Hồ Chí Minh trail, which passed through the Kingdom of Laos. The communists attacked South Vietnamese targets during the 1968 Tết Offensive. Although the campaign failed militarily, it shocked the American establishment, and turned US public opinion against the war. During the offensive, communist troops massacred over 3,000 civilians
1971 in the Vietnam War Exchanges in South Vietnam. President Nixon ordered the initiation of Operation Proud Deep Alpha, an intensive five-day bombing campaign against military targets in North Vietnam just north of they border above the 17th parallel of latitude. The number of U.S. military personnel in South Vietnam totaled 156,800, down from more than 500,000 three years earlier. 1971 in the Vietnam War U.S. military personnel in South Vietnam totaled 334,600 on 31 December 1970. The United States Congress adopted the revised Cooper-Church Amendment which prohibited the introduction of U.S. ground troops or advisers into Cambodia and declared that U.S. aid to Cambodia