That was initially designed to allow Reconstruction governments to deny the vote to white Southerners who had supported the Confederacy.
>Congress can’t pass a law (at least not a valid one) which >forces states to let felons vote. The 14th amendment protects >the states on this matter.
>That was initially designed to allow Reconstruction >governments to deny the vote to white Southerners who had >supported the Confederacy.
http://www.ncsl.org/research/elections-and-campaigns/felon-voting-rights.aspx