Can you clarify what you mean by "successful"? The black civil rights victories were in no way total, many created unforeseen problems for the black community, many forces within the civil rights community failed or were marginalized and used to discredit the movement, and in many ways such as incarceration rates the situation has arguably gotten worse.

The idea that the black civil rights movement largely succeeded and then ended is an historical fallacy. Are you asking specifically about desegregating the south, passing the civil rights act, and brown v. Board of Ed (which did not have a wholly positive outcome)?