Mpi / Getty Images College students at a sit-in in Little Rock, Arkansas, in 1962. Howard Sochurek / Getty Images Volunteer civil rights activists undergo tolerance training in preparation for sit-in demonstrations in Petersburg, Virginia, in May 1960. Here, NAACP student advisers David Gunter (left) and Leroy Hill (right) blow smoke into the face of Virginius Thornton. Bill Hudson / AP A 17-year-old civil rights demonstrator, defying an anti-parade ordinance of Birmingham, Alabama, is attacked by a police dog on May 3, 1963. On the afternoon of May 4, 1963, during a meeting at the White House with members of a political group, President Kennedy discussed this photo, which had appeared on the front page of that day's New York Times. Michael Ochs Archives / Getty Images Children are attacked by dogs and water cannons during a protest against segregation organized by Martin Luther King Jr. and Fred Shuttlesworth in May 1963 in Birmingham, Alabama. Bob Daugherty / AP Demonstrators march in front of an Indianapolis hotel where Alabama Gov. George Wallace is staying, as they are picketed by white youths carrying Confederate flags, on April 14, 1964. Robert W. Kelley / Getty Images A massive crowd is assembled on the National Mall in front of the Reflecting Pool and between the Lincoln and Washington monuments during the March on Washington for Jobs and Freedom on Aug. 28, 1963. It was at this rally that Martin Luther King Jr. delivered his "I Have a Dream" speech. Paul Schutzer / The LIFE Picture Collection / Getty Images Demonstrators march and sing together during the March on Washington for Jobs and Freedom on Aug. 28, 1963. Express Newspapers / Getty Images Young women clap and sing along to a freedom song between speeches at the March on Washington for Jobs and Freedom on Aug. 28, 1963. Robert W. Kelley / Getty Images Leaders of the March on Washington for Jobs and Freedom link arms on Aug. 28, 1963. Among those pictured, front row from left: John Lewis, Mathew Ahmann, Floyd B. McKissick, Martin Luther King Jr., Eugene Carson Blake, Cleveland Robinson, and Rabbi Joachim Prinz. John Dominis / Getty Images Participants cool their feet in the Lincoln Memorial Reflecting Pool during the March on Washington for Jobs and Freedom. AP Police drag demonstrators to an elevator in clearing the Justice Department building in Washington, DC, on March 9, 1965. Some 170 young people were removed from three corridors near the office of Attorney General Nicholas Katzenbach. Bettmann / Bettmann Archive Civil rights marchers carry an American flag upside down as they participate in the 50-mile Selma to Montgomery march on March 21, 1965. Chicago History Museum / Getty Images Participants walk in the Cicero march, a civil rights demonstration protesting racist housing policies in Cicero, Illinois, in 1966. AP A handcuffed anti–Vietnam War demonstrator is hauled away from the front of the Century Plaza Hotel in Los Angeles on June 23, 1967. A rock-throwing melee erupted as several thousand people protesting US involvement in the Vietnam War paraded in front of the hotel, where President Lyndon Johnson was giving a speech at a $500-a-plate dinner. David Hume Kennerly / Getty Images Wounded San Francisco State University demonstrators are restrained as they are taken away during the student strike protests against the Vietnam War in San Francisco on Dec. 3, 1968. Dick Swanson / Getty Images Peace demonstrators sit during a protest of the Vietnam War as military police in riot gear stand by on Jan. 1, 1967. Michael Rougier / Getty Images Robert F. Kennedy sits next to Cesar Chavez (visibly weak after a prolonged hunger strike) during a rally in support of the United Farm Workers union on March 1, 1968. Bettmann / Bettmann Archive Young men hold their burning draft cards aloft at an anti–Vietnam War demonstration in front of the Pentagon in Washington, DC, on Oct. 21, 1967. Harvey Silver / Getty Images An anti–Vietnam War march on Jan. 27, 1968. Bettmann / Bettmann Archive US National Guard troops block off a street in Memphis as civil rights marchers pass on March 29, 1968. Steve Starr / AP Heavily armed students of Cornell University leave a school building in Ithaca, New York, on April 20, 1969. The students had barricaded themselves in the building demanding a degree-granting African-American studies program. After a 36-hour sit-in, university administrators offered to drop some charges against the students and accelerate the opening of an African-American studies center. Santi Visalli / Getty Images A young woman offers a rose to uniformed military police officers outside the Democratic National Convention in Chicago on Aug. 28, 1968. Hulton Archive / Getty Images A young protester faces down armed police officers at an anti–Vietnam War demonstration outside the 1968 Democratic National Convention in Chicago. Julian Wasser / Getty Images Demonstrators swarm a statue in Grant Park during the 1968 Democratic National Convention. David Fenton / Getty Images A group of women march in support of the Black Panther Party of New Haven, Connecticut, in November 1969. Spencer Grant / Getty Images Marchers at a feminist parade salute outside the Old Cambridge Baptist Church in Cambridge, Massachusetts, in 1969. Bill Eppridge / Getty Images A demonstrator protests at the presidential inauguration of Richard Nixon in Washington, DC, on Jan. 20, 1969.