The 15th Amendment states, "The right of citizens of the United States to vote shall not be denied or abridged by the United States or by any State on account of race, color or previous condition of servitude." It also grants Congress the right to enforce this amendment by the use of appropriate legislation. It was the last of the Reconstruction Amendments, adopted on March 3, 1870.
After the Civil War, many southern states attempted to resist granting voting rights to African Americans through various means. One common method was the "grandfather clause," which stated that someone had the right to vote if his grandfather had the right to vote. Since none of the ex-slaves had grandfathers who could have voted, they were kept out of the electoral process. Poll taxes collected in exchange for the right to vote and literacy tests were also tools these states used to limit voting rights to white citizens. African Americans were also kept away from the ballot box by the threat of violence from groups such as the Ku Klux Klan.
The first African-American voter to cast a ballot under the 15th Amendment's protection was Thomas Mundy Peterson. On March 31, 1870, he voted in a mayoral election in New Jersey.