The movement against the involvement of the United States in the Vietnam War began in the U.S. with demonstrations in 1964 and grew in strength in later years. The U.S. became polarized between those who advocated continued involvement in Vietnam and those who wanted peace.
Many in the peace movement were students, mothers, or anti-establishment hippies. Opposition grew with participation by the African-American civil rights, women's liberation, and Chicago movements, and sectors of organized labor. Additional involvement came from many other groups, including educators, clergy, academics, journalists, lawyers, physicians (such as Benjamin Spock ), Civil Rights Movement leaders and military veterans. Opposition consisted mainly of peaceful, nonviolent events; few events were deliberately provocative and violent. In some cases, police used violent tactics against demonstrators. By 1967, according to Gallup Polls , an increasing majority of Americans considered US military involvement in Vietnam to be a mistake, echoed decades later by the then head of American war planning, former U.S. Secretary of Defense Robert McNamara.