The correct response would be:
Over time, the gains made by the Fifteenth Amendment were eroded.
The Fifteenth Amendment, ratified in 1870, granted African American men the right to vote, but over the following decades, various political and social mechanisms (such as Jim Crow laws, literacy tests, poll taxes, and other forms of discrimination) were implemented that effectively suppressed Black voters and eroded the gains made by the amendment in South Carolina and across the Southern United States.