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 ("Hawks"), and those who wanted peace ("Doves").
Many in the peace movement were students, mothers, or long-haired anti-establishment types, says Wikipedia.
Also involved were educators, clergy, academics, journalists, lawyers, physicians (such as Benjamin Spock and Justin Newlan), military veterans, and ordinary Americans.
Expressions of opposition events ranged from peaceful nonviolent demonstrations to radical displays of violence.
In 1967, Civil rights leader Martin Luther King led a march of 5,000 against the war in Chicago, Illinois. He was assassinated in 1968.
Also in 1967 400,000 people marched from Central Park to the UN building in New York City to protest the war, where they were addressed by critics of the war such as Benjamin Spock and Martin Luther King. On the same date 100,000 marched in San Francisco.
In 1968 the Tet Offensive was launched and resulted in much higher casualties and changed perceptions of the state of the war.
In 1969 crowds estimated up to half a million people participated in an anti-war demonstration in Washington, D.C. A similar demonstration was held in San Francisco.
Protests continued - against Nixon's bombing of N Vietnam - through 1972.