The Reconstruction period that followed America's Civil War was one of the worst, most violent eras in American history. During that time, thousands of African-Americans were killed by domestic terrorists like the Ku Klux Klan who tried to reinforce antebellum policies of white supremacy. For many historians, one of the worst examples of this violence occurred 143 years ago today: the Colfax Massacre of 1873.

Immediately after the end of the Civil War, different factions began fighting over power. Bitter over the Confederacy’s loss, many white Southern Democrats tried their best to continue disenfranchising and restricting the rights of former slaves. At the same time, insurgent, white supremacist groups terrorized African-Americans throughout the South. In Louisiana, the fight over the postwar government was particularly bloody, as PBS’ American Experience series explores.

Simmering resentments between Southern Democrats, most former slave owners, and the Republican-dominated federal government exploded in the 1872 election for Louisiana’s governor. The ballot resulted in a hotly contested split between the Republican and Democratic candidates, and when President Ulysses S. Grant sent federal troops to support the Republican candidate, white southerners rebelled and formed a heavily armed insurgent army called the “White League.” Similar to the Ku Klux Klan, the White League was a paramilitary group that intimidated and attacked blacks and white Republicans across the state, Henry Louis Gates, Jr. writes for the Root.

Out of fear that local Democrats might try to seize control of the Grant Parish regional government, which was almost evenly split between black and white citizens, an all-black militia took control of the local courthouse in April 1873. Soon after, a mob of more than 150 white men, most former Confederate soldiers and members of the Ku Klux Klan and the White League arrived and surrounded the courthouse, Bill Decker writes for the Lafayette Advertiser. After firing a cannon on the militiamen inside the courthouse on April 13, the two forces fired at each other until the black defenders were forced to surrender. But when they surrendered, the white mob murdered many of the black men, shooting at them and hanging some. Historians aren’t sure how many people died in the end, but while records show that the massacre resulted in the deaths of three white men, it's estimated that anywhere from 60 to 150 African-Americans were killed.

“The bloodiest single instance of racial carnage in the Reconstruction era, the Colfax massacre taught many lessons, including the lengths to which some opponents of Reconstruction would go to regain their accustomed authority,” historian Eric Foner writes in Reconstruction: America's Unfinished Revolution, 1863–1877. “Among blacks in Louisiana, the incident was long remembered as proof that in any large confrontation, they stood at a fatal disadvantage.”

While the massacre made headlines across the country and 97 members of the white mob were indicted, in the end only nine men were charged of violating the Enforcement Acts of 1870 and 1871, sometimes known as the Klu Klux Klan Acts, intended to guarantee the rights of freedmen under the 14th and 15th Amendments. Lawyers for the victims believed that they had a better chance of bringing the ringleaders to justice in a federal court citing conspiracy convictions, instead of charging them with murder, which would have been tried in the heavily Democratic state courts. But the plan backfired. The defendants appealed, and when the case eventually came before the Supreme Court in 1876, the justices overturned the lower courts’ convictions, ruling that the Enforcement Acts applied only to actions by the state, not by individuals, Decker writes.

This ruling essentially neutered the federal government’s ability to prosecute hate crimes committed against African-Americans. Without the threat of being tried for treason in federal court, white supremacists now only had to look for legal loopholes and corrupt officials to continue targeting their victims, Gates reports. Meanwhile, principles of segregation were beginning to work their ways into law, with Plessy v. Ferguson officially codifying “separate but equal” just 20 years later.

The Colfax Massacre was more or less ignored until the 1920s, when local officials raised a monument honoring the three white men who died in the attack on the courthouse, which called the battle a “riot.” In 1951, officials marked the site of the massacre with a plaque, once again calling it a riot that “marked the end of carpetbag misrule in the South.” The plaque still stands to this day.