Once the Civil War ended, the Fifteenth Amendment was passed. This amendment guaranteed citizens the right to vote, without any kind of restriction based on racial issues or previous conditions of slavery.
Now, after the Reconstruction was over, when the Democrats regained control of the southern states, the racist governments that were imposed in that period established a series of prohibitions and limitations by means of which it became practically impossible for African-Americans they could vote freely: on the one hand, they imposed so-called poll taxes, by means of which it was necessary to pay a high tax in order to vote (thereby limiting the right to vote of the lower classes, predominantly composed of African-Americans); On the other hand, the Grandfather's Clause was established, which allowed voting only for people whose ancestors had also previously voted. Even other measures of lesser application were the literacy tests, which also limited the right to vote only for people with a certain academic level.