In 1868, Florida’s white elites faced a threat every bit as grave as the Civil War that had ended in Confederate defeat three years earlier. Congress had just forced Florida to rewrite its constitution to allow every man the right to vote. But adding thousands of newly eligible black residents to the rolls would abruptly make whites a voting minority.

The old guard’s only hope was to somehow ban black voters without violating Reconstruction acts passed by Congress after the Civil War. Huddled in Tallahassee backrooms throughout that cool January, they found just the ticket: a lifetime voting ban on anyone with a felony conviction. Combined with postwar laws that made it comically easy to saddle black residents with criminal records, legislators knew they could suppress black votes indefinitely.

Or at least for a century and a half. On Tuesday, Florida voted to end that 150-year-old ban by backing Amendment 4, which will return voting rights to more than 1 million Floridians who have already served out their sentences. The amendment garnered 64 percent of the vote.

Historians say the vote also ends a law with roots so blatantly racist that one state leader later boasted that the postwar constitution would prevent Florida from becoming taken over by blacks, using a racial slur to describe them.

“Their intent was quite clear: to eliminate as many black voters as possible,” said Darryl Paulson, an emeritus professor of government at the University of South Florida St. Petersburg.

The ban was remarkably effective at doing so, even 150 years later. As of 2016, more than 1 in 5 black Floridians couldn’t vote thanks to the rule, according to an analysis by the Sentencing Project.

“We can’t have a democracy with permanent second-class citizens,” Howard Simon, the American Civil Liberty Union’s Florida executive director, told the Miami Herald.

The origins of Florida’s ban trace back to the blood-soaked days just after Robert E. Lee’s surrender. As Southern states like Florida rejoined the Union, many tried to explicitly ban black voters. Florida’s first post-war state constitution in 1865 only gave the right to vote to “free white males,” according to a 2016 report by the Brennan Center for Justice.

White lawmakers had a tactical reason to fear newly empowered black voters. While blacks made up about 45 percent of Florida’s population after the war, thousands of white residents had lost their right to vote over their Confederate ties. By 1867, Paulson found, there were 15,434 black voters registered in Florida and just 11,148 who were white.

Even as Congress forced southern states’ hand with the 13th, 14th and 15th Amendments, which freed slaves and gave them citizenship and the right to vote, Florida legislators laid the groundwork to disenfranchise those black residents. In 1865, the state passed a package of laws known as the “Black Codes” that upped the penalties for charges easy to pin on freed blacks, including assaulting a white woman, disobedience and “vagrancy,” a crime with such a broad definition nearly anyone could be charged.

That was the perfect precursor to including a voting ban on felons in the 1868 constitution. Legislators also included a more broad voting prohibition against anyone convicted of more minor “Black Code” crimes, like larceny.

“Felony disenfranchisement was a way of reducing the effect of the despised black suffrage that Conservatives knew they had no alternative but to accept,” wrote historian Jerrell Shofner in a piece on the drafting of Florida’s 1868 constitution.

The law was just one among many the state adopted to keep African-Americans away from the polls. In 1889, Florida became the first state to adopt a poll tax, charging $2 annually with full knowledge that poor blacks would be disproportionately affected. It later adopted literacy laws and residency rules aimed at cutting out black voters, Paulson said.

Those efforts were astoundingly effective. As little as 3 percent of black Floridians were registered to vote in 1940. By 1961 in Gadsden County in Florida’s Panhandle, there were 12,261 African Americans old enough to vote — but only seven were registered, according to the Brennan Center.

Most of those outright discriminatory rules ended in the civil rights era of the 1960s, but Florida’s felony voting ban continued. In 1968, Florida legislators watered down the rule but kept the ban on felons. When black voters took the state to court, a panel from the 11th U.S. Circuit Court of Appeals found there was “racial animus” behind the original law, the Brennan Center noted, and no compelling reason to keep it on the books. But that decision was later reversed by the full court sitting en banc.

More recently, then-Republican Gov. Charlie Crist eased the rules for many felons to get their rights back, restoring tens of thousands to the electoral rolls. But Gov. Rick Scott erased those reforms in 2011, adding a new five-year waiting period and requiring felons to appear before a clemency board in person to plead their case.

That has led to a system so bizarre that John Oliver panned it as “insane” in a recent piece on “Last Week Tonight.” “It may be the dumbest thing about Florida, which is saying something,” Oliver said.

As a backlog grew of more than 10,000 people waiting to be heard by the clemency board, Scott’s decisions neatly fit the historic patterns of the ban. The Palm Beach Post found that Scott returned voting rights to three times as many white men as black men.

Amendment 4 nabbed more than 1.1 million signatures to land on Tuesday’s statewide ballot and found support from a surprising breadth of backers, from the Koch Brothers-funded Freedom Partners to the ACLU. But it did face opposition from mainstream GOP candidates, including Scott, who remains ahead in his Senate bid as of early Wednesday, and Florida’s governor-elect Ron DeSantis. Both argued the amendment was too broad, although it excludes anyone convicted of murder or sexual crimes.

In the end, Amendment 4 easily crossed the state’s 60 percent threshold — a victory that should stand as a rebuke to decades of racial oppression, said Paulson.

“It has been a real embarrassment for Florida to be leader in keeping people away from voting,” Paulson said. “The United States should do everything humanly possible to make voting as accessible as possible to everyone.”