"The voting rights of black Americans have been effectively guaranteed only since passage of the Voting Rights Act in 1965 (P.L. 89-110), despite a constitutional amendment adopted nearly 100 years earlier that said '[t]he right of citizens of the United States to vote shall not be denied or abridged by the United States or any State on account of race, color, or previous condition of servitude.' Initially, the Fifteenth Amendment profoundly changed electoral politics in the country and particularly in the former slave states. The first black Members of Congress were chosen in 1870 from Mississippi and South Carolina, respectively, and hundreds of black officeholders at all levels were elected in the following years. By the turn of the 20th century, however, a little more than 20 years after the Reconstruction era ended, no African Americans served in Congress and all of the former Confederate states had rewritten their constitutions to exclude African Americans from voting. Despite the efforts of the National Association for the Advancement of Colored People (NAACP), founded in 1909, the civil rights movement, and congressional intervention with the enactments of the Civil Rights Acts of 1957, 1960, and 1964, the status quo of black disenfranchisement remained entrenched and resistant to wholesale change until the adoption of the Voting Rights Act."
CRS Report for Congress, R43626
Federation of American Scientists: http://www.fas.org/