The 15th Amendment to the Constitution of the United States, ratified in 1870, prohibits federal or state governments from infringing on a citizen's right to vote "on account of race, color, or previous condition of servitude." This amendment is the last of three so-called Reconstruction amendments ratified in the aftermath of the Civil War to abolish slavery and firmly establish minority civil rights. The 15th Amendment allowed the federal government to legislate qualifications for voting, a right formerly left to the states. Its ratification, however, had little impact for almost a century and had virtually no effect in the South where various methods from terrorism to the poll tax and grandfather clause were employed to keep blacks from voting. Various actions of Congress and the Supreme Court eventually struck down voting restrictions. In Smith v. Allwright (1944), for example, the Court held voting-rights discrimination in primaries to be unconstitutional on the basis of the 15th Amendment. Other cases blocked the discriminatory use of reapportionment and property and residence requirements. Congress passed the Civil Rights Act of 1957, establishing a commission to investigate voting discrimination, and in 1965 the Voting Rights Act (extended in 1970, 1975, and 1982) was passed to increase black voter registration by empowering the Justice Department to closely monitor voting qualifications.