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
Vietnam War artillery, and airstrikes. The U.S. conducted a large-scale strategic bombing campaign against North Vietnam. Following the Tết Offensive, U.S. forces began withdrawal under the Vietnamization phase; the Army of the Republic of Vietnam unconventional and conventional capabilities increased following a period of neglect and became modeled on heavy fire-power focused doctrines like US forces. Operations crossed international borders: bordering areas of Laos and Cambodia were used by North Vietnam as supply routes and were heavily bombed by U.S. forces. Gradual withdrawal of U.S. ground forces began as part of "Vietnamization", which aimed to end American involvement in the war while