After the American Civil War in 1865, where 4 million slaves got their freedom and for the first time they were able to enjoy liberty of speech and movement, education for their children, the right of a fair trial as well as all the privileges of American citizenship, a reconstruction period took place.
In such reconstruction period, Congress acted to prevent Southerners from going back to the white supremacy, by placing federal troops to protect the rights of black citizens. But when reconstruction ended in 1877 federal troops were withdrawn and thus white supremacy returned to the old Confederate states. Consequently, black voting fell off because of threats mostly by white employers and the secret organization determined on preserving white supremacy known as Ku Klux Klan.