How did southern blacks lose rights in the years after the thirteenth fourteenth and fifteenth amendments

Southern blacks lost rights in the years after the thirteenth fourteenth and fifteenth amendments because the North withdrew many of the troops that had been enforcing these new laws, leaving southerners to pass a series of Jim Crow laws that prohibited blacks from voting, gaining jobs, and a variety of other things in the South. 

Ithink its trade and commernce let me know if im wrong