U.S. military involvement in Vietnam accelerated after the passing of the Gulf of Tonkin Resolution by congress in August 1964. The resolution gave President Lyndon B. Johnson the power to use conventional military force in Southeast Asia without a formal declaration of war. By 1968, the United States' military presence had reached its peak at over 500,000 troops deployed. Following the Tet Offensive by the North Vietnamese and Viet Cong in early 1968, U.S. public opinion shifted dramatically against the war and President Johnson announced his intention to scale back U.S. military presence in the region.
As U.S. troops left Southeast Asia, there was an attempt to manage a 'vietnamization' of the conflict, whereby the South Vietnamese military would receive aid and training from the U.S. in order to fill the gap left by the withdrawing U.S. forces. As the numbers of U.S. service personnel dwindled, so too did the number of battle deaths from the conflict, which had also peaked in 1968. The last U.S. military forces left the region in 1973, with the final U.S. personnel leaving with the Fall of Saigon to the communist forces in April 1975.