What accomplishments of the civil rights movement were achieved through nonviolent means? why, despite these accomplishments, did some african americans come to reject nonviolence?

Nonviolence achieved desegregation of institutions and transportation such as bus lines. It also contributed to the passage of the Civil Rights Act and the Voting Rights Act. 

Some rejected nonviolence because despite the wins, blacks were still being arrested and beaten at high rates. They were met with violence and an expectation to work within the rules set by whites.