From 1870, when the 15th Amendment banned racial discrimination in voting, until 1965, states and localities across the former Confederacy adopted poll taxes, literacy tests and "good character" and “moral turpitude” requirements that worked to exclude African-Americans from the voter rolls. It was common in the deep south then to find few if any blacks registered to vote even in majority-black counties.
Court decisions, the civil rights movement, and the Voting Rights Act of 1965 changed that, leading to the election of hundreds of African-Americans to city and county councils, state legislatures, and other offices.
Particularly critical was the Voting Rights Act’s requirement that designated states and localities get federal approval in advance of any changes in their voting laws or regulations. The Brennan Center for Justice says that between 1982 and 2006, federal officials used this “preclearance” requirement to block implementation of more than 1,000 discriminatory voting changes. The requirement essentially was gutted by the Supreme Court in 2013, though the justices said Congress can restore it.