The 1965 Selma to Montgomery March was the most controversial and bloody march in the history of Black Civil Rights. The march, now crudely nicknamed "Bloody Sunday" was supposed to let the black population of Selma vote, but instead turned into a full-on bust up between the protesters and the white racists and extremists.
Throughout March of 1965, a group of demonstrators faced violence as they attempted to march from Selma, Alabama, to Montgomery, Alabama, to demand the right to vote for black people. They aimed their sights at Selma, as 90% of it's population were black, and yet only 1% were able to vote. One of the pivotal days was March 7, when 17 people were injured by police, including future Congressman John Lewis. Since that time, March 7th has been known as "Bloody Sunday." The march has been reenacted many times on its anniversary. It is about 50 miles (80 kilometers) from Selma to Montgomery, so it was a very long walk for the protesters.
Above: Protesters and Police standing off.
After being heckled by white police and mobs of racists, finally, the protesters (under the protection of the National Guard) completed the march, walking for three straight days, in the night as well as the day. This was a hidden catalyst, unbeknownst to the protesters, for the Voting Rights Act that was passed that same year.