Key moment: In October 1967, massive crowds converged in Washington, D.C., to protest the Vietnam War.
Historical significance: Although a majority of Americans were against the Vietnam War, college students were at the forefront of the opposition and campus protests were common. On May 4, 1970, four Kent State University students were killed after the Ohio National Guard fired into a crowd of anti-war demonstrators. Photographs of the dead and injured students further fueled opposition to the war and the Nixon administration. (Photo courtesy Library of Congress)