During an 18-hour period between May 31 and June 1, 1921, Tulsa, Oklahoma, became the setting of one of the most devastating racial massacres to happen on U.S. soil. The Tulsa Race Massacre killed dozens, if not hundreds, of people, and left a permanent scar on one the most vibrant Black communities in America.

Despite the impact of the event, it's still omitted from textbooks today. Here are some facts you should know about the Tulsa Race Massacre.

1. Tulsa’s African-American business district was known as “Black wall Street.”

In early 1921, Tulsa’s Greenwood neighborhood was home to the majority of the city's 10,000 Black residents, making it the second-largest African-American community in Oklahoma. It was also one of America’s wealthiest Black neighborhoods at the time. It boasted a library branch, two newspapers, and a prosperous business district dubbed “Black Wall Street.”

2. There’s some confusion over what sparked the Tulsa Race Massacre.

Though Tulsa was an affluent town, it was embroiled in crime and racial tensions. White mobs were known to lynch people they suspected of crimes in the name of vigilante justice, and the police did little to stop them. These lynch mobs barely needed a reason to launch a crusade if their target was Black.

On May 31, 1921, a Black teenager named Dick Rowland was arrested following an incident that occurred in the Drexel Building on South Main Street the previous day. After he entered the elevator of the office building, the elevator operator—a white woman named Sarah Page—screamed, and Rowland fled. While it was this incident that sparked the Tulsa Race Massacre, it's not exactly clear what transpired between Rowland and Page. The most common story is that Rowland stepped on Page's foot, causing her to yelp in pain. But the Tulsa Tribune had a different story; it reported that Rowland had tried to rape Page, and a mob of angry white residents showed up at the courthouse demanding the police hand him over.

3. It's unclear just how many people were killed during the Tulsa Race Massacre, but it's one of America's most deadly incidents of racial violence.

Law enforcement refused to release Rowland to the mob, but the crowd didn’t disperse. A group of armed Black men showed up at the courthouse to offer the police their support in protecting Rowland. Tensions rose between the two groups and shots were fired, kicking off a riot that would last for approximately 18 hours, until June 1.

The mob of hundreds of angry white Tulsans infiltrated Greenwood, where they looted and burned homes and businesses and attacked unarmed residents. More than 1200 houses and buildings were burned, including a school, a library, a hospital, churches, and both of Greenwood's newspapers. Between 50 and 300 people were likely killed in the massacre, making it one of the deadliest incidents of racial violence in U.S. history.

4. Police may have encouraged violence during the Tulsa Race Massacre.

Tulsa police weren’t able to control the riot, and they may have even helped fuel it. According to an eyewitness account, the authorities armed and deputized white members of the mob and used racial slurs when encouraging them to go after Black Tulsans. When the National Guard eventually arrived to stop the violence, they mainly focused on protecting a white neighborhood from imaginary threats instead of attending to the Black neighborhood that was on fire.

5. There was an effort to erase the Tulsa Race Massacre from history.

The Tulsa Race Massacre is missing from many school curriculums and history books today. That’s because in the years that followed, there was a concerted effort to suppress the story. The Tulsa Tribune article accusing Dick Rowland of assault, which originally ran as a front-page story, was removed from bound volumes of the paper, and accounts of the incident were wiped from police and state militia archives. In the decades after the massacre, there were no public memorials or other events commemorating it.

It wasn't until 1997—a full 76 years after the event—that the government formed an official Race Riot Commission to investigate the details of the Tulsa Race Massacre. In 2020, just one year away from the 100-year anniversary, an extensive curriculum on the massacre was finally provided to Oklahoma school districts.