The 1968 Tet Offensive weakened American support of the Vietnam War and triggered the slow process of withdrawal of American military forces. It marked the turning point in the Vietnam War.
On January 31, 1968, 70,000 North Vietnamese and Viet Cong forces launched an attack with the intent of breaking the alliance between the United States and the South Vietnamese and forcing the United States to negotiate or withdraw altogether. As vivid reports of the fighting were broadcast in the United States, it became clear to the U.S. public that the continued fighting had created a credibility gap between the administration's optimistic reports and the harsh reality of the war, and American support for the war dwindled.
According to the Department of State, after the third phase of attacks ended in August, U.S. generals requested additional troops in order to mount a counteroffensive, but President Johnson vetoed the request because he recognized that adding more troops to the war was untenable in Vietnam and unpopular in the United States. In March of 1969, Johnson announced he was not running for re-election, and left the peace negotiations to Nixon, who finally withdrew the last of the American forces in August 1974.