section_path: From confrontation to détente (1962–1979)/Vietnam War
section_name: Vietnam War
paragraph_text: Vietnam War
  
  Under President John F. Kennedy, US troop levels in Vietnam grew under the Military Assistance Advisory Group program from just under a thousand in 1959 to 16,000 in 1963. South Vietnamese President Ngo Dinh Diem's heavy-handed crackdown on Buddhist monks in 1963 led the US to endorse a deadly military coup against Diem. The war escalated further in 1964 following the controversial Gulf of Tonkin incident, in which a US destroyer was alleged to have clashed with North Vietnamese fast attack craft. The Gulf of Tonkin Resolution gave President Lyndon B. Johnson broad authorization to increase US military presence, deploying ground combat units for the first time and increasing troop levels to 184,000. Soviet leader Leonid Brezhnev responded by reversing Khrushchev's policy of disengagement and increasing aid to the North Vietnamese, hoping to entice the North from its pro-Chinese position. The USSR discouraged further escalation of the war, however, providing just enough military assistance to tie up American forces. From this point, the People's Army of Vietnam (PAVN), also known as the North Vietnamese Army (NVA), engaged in more conventional warfare with US and South Vietnamese forces.
  
  The Tet Offensive of 1968 proved to be the turning point of the war. Despite years of American tutelage and aid, the South Vietnamese forces were unable to withstand the communist offensive and the task fell to US forces instead. Tet showed that the end of US involvement was not in sight, increasing domestic skepticism of the war and giving rise to what was referred to as the Vietnam Syndrome, a public aversion to American overseas military involvements. Nonetheless, operations continued to cross international boundaries: bordering areas of Laos and Cambodia were used by North Vietnam as supply routes, and were heavily bombed by US forces.
  
  At the same time, in 1963–1965, American domestic politics saw the triumph of liberalism. According to historian Joseph Crespino: