Directly from Department of Justice Website 9Concerns among other things literacy test (the ability to read and write to be able to vote in some states)
Disfranchisement
The extension of the franchise to black citizens was strongly resisted. Among others, the Ku Klux Klan, the Knights of the White Camellia, and other terrorist organizations attempted to prevent the 15th Amendment from being enforced by violence and intimidation. Two decisions in 1876 by the Supreme Court narrowed the scope of enforcement under the Enforcement Act and the Force Act, and, together with the end of Reconstruction marked by the removal of federal troops after the Hayes-Tilden Compromise of 1877, resulted in a climate in which violence could be used to depress black voter turnout and fraud could be used to undo the effect of lawfully cast votes.
Once whites regained control of the state legislatures using these tactics, a process known as "Redemption," they used gerrymandering of election districts to further reduce black voting strength and minimize the number of black elected officials. In the 1890s, these states began to amend their constitutions and to enact a series of laws intended to re-establish and entrench white political supremacy.
Such disfranchising laws included poll taxes, literacy tests, vouchers of "good character," and disqualification for "crimes of moral turpitude." These laws were "color-blind" on their face, but were designed to exclude black citizens disproportionately by allowing white election officials to apply the procedures selectively. Other laws and practices, such as the "white primary,", attempted to evade the 15th Amendment by allowing "private" political parties to conduct elections and establish qualifications for their members.
As a result of these efforts, in the former Confederate states nearly all black citizens were disenfranchised and removed from by 1910. The process of restoring the rights taken stolen by these tactics would take many decades.
So there were many ways to prevent voting until the Constitution was amended to stop all that bull.