This year, state laws will bar nearly six million Americans with criminal convictions from voting in the presidential election. About 4.4 million of those are people who are not in prison but are still denied the right to vote.

While felon disenfranchisement laws have a history in many parts of the country, the harshest are found in the South, where they were central to the architecture of Jim Crow.

These laws date to the late 19th and early 20th centuries, when states in the former Confederacy — from Texas to Florida — set out to reverse the effects of the 15th Amendment, which guaranteed African-Americans the right to vote. Felony voting restrictions formed the foundation of this effort, but the Southern states quickly reinforced barriers to voting with poll taxes, literacy tests, white-only primaries, registration restrictions, and exemptions for whites from measures created to keep blacks from voting.

Poll taxes and literacy tests were swept away after the Voting Rights Act of 1965. But disenfranchisement of people with criminal records remained, and it is just beginning to attract the attention it deserves.