The correct answer is: "inequality".
The Reconstruction Amendments (13th, 14th and 15th) had abolished slavery, granted equal protection and rights to US citizens and prohibited the goverment, at the federal and state levels, from impeding any citizen to vote because of their race, color of skin or previous condition of servitude (respectively).
But in practice, many Southern states tried to circumvent the mentioned provisions by enacting the so-called Jim Crow laws. These tried to indirectly prevent African Americans from voting by setting requirements in order to have access to vote, such as, a minimum income level or passing a literacy test. The majority of people who did not meet the predefined criteria and who not allowed to vote were black citizens.
