Throughout most of the nineteenth and twentieth centuries, most African Americans were prevented from voting in many Southern states despite the Fifteenth Amendment, which extended the right to vote to African American males. Southern states were able to take this action because

They passed the Jim Crow Laws.

Explanation:

Jim Crow laws was the widespread unofficial name of laws on racial segregation in some southern states during the post-Reconstruction period, that went from 1890 to 1964.

After the Civil War, which freed blacks from slavery, the federal government took steps to ensure their civil and political rights through the passing of the 13th, 14th, 15th amendments to the Constitution, and Civil Rights Acts of 1866 and 1875. In response, Southern Democrats passed local laws that severely restricted the rights of the black minority, as well as Indians who refused deportation to Oklahoma and remained under the jurisdiction of the US government in the southeastern states.

The beginning of the "Jim Crow Laws" era is considered to be 1890, when racial segregation on the railroad was introduced in Louisiana. By 1915, every southern state had passed laws that established segregation in educational institutions, hotels, shops, restaurants, hospitals, transportation, and toilets. There were also restrictions related to voting: electoral tax and literacy test, which applied only to blacks.

what’s your question

regarding the law, the 15th amendment was specifically designed thinking in the rights of black free men.

even though ratified on february 3, 1870, the promise of the 15th amendment would not be fully applied for a long time.poll taxes and literacy tests would allow southern states disenfranchise african americans. only in 1965 the voting rights for african americans would be actually able to vote in the south.

in 1965, president johnson signed the voting rights act, which aimed to overcome legal barriers that prevented african americans from voting as it was guaranteed by the 15th amendment to the u.s. constitution.