Henry David Thoreau gave the idea its name in an 1849 essay first titled Resistance to Civil Government. He had spent a night in jail in 1846 for refusing to pay a poll tax in protest of slavery and the Mexican-American War. Mohandas Gandhi and Martin Luther King Jr. later built mass movements on the idea.
The civil rights movement used civil disobedience on purpose. In 1955, Rosa Parks refused to give up her seat on a Montgomery bus and was arrested. Sit-in students broke segregation laws at lunch counters. Freedom Riders in 1961 rode interstate buses in defiance of local segregation practices. In his 1963 Letter from Birmingham Jail, King argued that people have a moral responsibility to disobey unjust laws.
Civil disobedience matters because many laws once enforced by police and courts, including segregation statutes, were later recognized as unjust. The willingness to face arrest exposed that injustice to the public and to the courts.