Selma, AL, circa early 1960s:
For decades, the Deep South had resisted the federal government's insistence that black American citizens be afforded the same rights as their white counterparts. Their response was "Jim Crow", which was a euphemism for "separate, but equal", which was an oxymoron. Along with that was a conspiracy from the local level all the way up to the top of the state government to deny black citizens the right to vote. It was bad enough that it required a constitutional amendment (the 24th - ratified in 1964) to remove most of the impediments to voting.
The Civil Rights Movement under the guidance of Martin Luther King (who studied Ghandi) used non-violent protest and "civil disobedience" (sitting at "whites-only" lunch counters) to push the point that they were not breaking the law - they were only trying to assert their rights. For that, they were brutally suppressed. Attack dogs, water cannon, and beatings from the police, as well as brutal attacks from citizens did not dissuade them.