The answer is debt peonage system.
Whites did not want African Americans to have political power. How did Southern politicians prevent blacks from voting? Here are several examples:
Poll tax—People were required to pay a special fee before being allowed to vote. Blacks and poor whites in the South often could not afford to pay the poll tax and thus could not vote.
Literacy test—Some states required voters to pass a literacy test. Measures were taken to make sure that African Americans did not pass. For example, African Americans were given more difficult tests than those given to whites. Other times, their tests were written in a foreign language.
Grandfather clauses—This had the effect of allowing a white man to vote even if he had failed to pay the poll tax or pass the literacy test. He could vote so long as he or his ancestors had been eligible to vote prior to January 1, 1867. Before this date, freed blacks had not been granted suffrage.
White primary—Blacks were excluded from taking part in the Democratic political party primaries.