Still, it said, United States disenfranchisement laws "remain some of the most restrictive in the world."

Immigrants were another common target of disenfranchisement laws.

The disenfranchisement laws do that in 13 states, where a felony conviction can result in a lifetime ban on voting.

Since the 2000 election, several states, including New Mexico, Delaware and Maryland, have abandoned or modified disenfranchisement laws.

"Most affected were Southern states," Uggen wrote, "where disenfranchisement laws clearly benefited Republicans."

Alabama has one of the nation's most sweeping disenfranchisement laws for felons, who are stripped of the vote for the rest of their lives.

Because most felons are likely to be poor and members of racial minority groups, they wrote in their study, "disenfranchisement laws tend to take votes from Democratic candidates."

Black people who fled the South found that the states in the North had also begun to adopt disenfranchisement laws as their black populations grew.

A recent study estimated that disenfranchisement laws now deprive as many as five million Americans of the right to vote.

States have the right to enact and enforce such sensible disenfranchisement laws, which apply to all felons regardless of race.