(CNN) Thelma Shepherd was riding back to her Chicago apartment on July 27, 1919, when her streetcar came under attack. Black and white men hurled rocks at each other and at the passing vehicle. The 19-year-old who had recently left the South for a job in the bustling city didn't know it, but she had witnessed one of the most violent clashes of the "Red Summer."

The drivers made no stops and dropped all the passengers off at the end of the line, her granddaughter, Claire Hartfield, remembers her saying years later.

"She was new to the city," Hartfield recalls. "She wasn't really aware of the tensions that had been building. She was just enjoying some of the excitement of being in a really big city.

"It was an ... eye-opener for her."

But other passengers on the next routes weren't lucky enough to escape.

"Street-car routes, especially transfer points, were thronged with white people of all ages," a 1922 report by the Chicago Commission on Race Relations says. Black passengers were dragged out to the street, beaten and kicked.

Over the next few days, white mobs stormed the streets attacking blacks indiscriminately. Thirty-eight people were killed, 23 of whom were black, and more than 500 were injured, the commission on race relations said.

In this 1919 photo provided by the Chicago History Museum, a victim is stoned and bludgeoned under a corner of a house during the race riots in Chicago.

Chicago wasn't the only city besieged by mob violence in the months after World War I. White gangs were eager to maintain Jim Crow-era laws but African-American soldiers returning from the war were demanding their rights and an end to second-class citizenship. Between late 1918 and late 1919, the US saw 10 major anti-black riots, dozens of minor, racially charged clashes and almost 100 lynchings, writes David F. Krugler, author of "1919, The Year of Racial Violence: How African Americans Fought Back."

Scores of black men and women were killed that year in racial violence. Nobody knows how many. The official death toll, Krugler says, was more than 150 people -- the majority of whom were black -- across the country between late 1918 and 1919. The Arkansas State Archives says 200 blacks were killed in Arkansas alone over several days in September 1919.

"Overwhelmingly, it was whites attacking blacks," Krugler told CNN.

But for nearly 100 years, the "Red Summer" as it was called by NAACP field secretary James Weldon Johnson because of its explosive violence and bloodshed, went overlooked and forgotten.

"The Red Summer doesn't fit into the stories we tell ourselves about US history," Krugler says. "It's also a very prominent example of another feature of American history that we don't like to fully acknowledge."

In this 1919 photo provided by the Chicago History Museum, a crowd gathers at a house that has been vandalized and looted during the race riots in Chicago. Some of the crowd is posing inside broken windows, others are standing on the lawn.

Until today, very little has been recorded about the violence that occurred.

"When I wrote my book, people wouldn't talk about it," Cameron McWhirter, author of "Red Summer: The Summer of 1919 and the Awakening of Black America," told CNN. "People have spent a lot of time not focusing on it. (There's) a lot of focus now on trying to uncover this part of history."

A panicky time for white America

"A lot of people would think that 1919 was this heroic happy time for America because we just won the war," McWhirter says. "But this wasn't the case. It was a panicky time for America."

There were strikes across the country, rising prices and unemployment, returning veterans who couldn't find a job and the spread of Communism.

"In the midst of all that, we have America's racial problem," he says.

While hundreds of thousands of soldiers had been fighting across the ocean, some 5 million African Americans -- including Shepherd -- had migrated from the South to cities like Chicago, where factory owners welcomed the cheaper labor and where, according to McWhirter, the newcomers were being treated "slightly better."

In this 1919 photo provided by the Chicago History Museum, police look through a broken window of a house during the race riots in Chicago. Broken furniture is strewn about the front yard.

"Overall, it was not what we'd consider equity but it was better than what they had in the South," he said.

But the population pump caused extreme racial tensions as black neighborhoods began to expand and blacks were no longer confined to designated areas.

Tensions grew in the South, too, where sharecroppers began making money and buying land and homes.

"So all these things that were theoretically good for black people at that time became sources of violence," McWhirter says.

And white gangs began to attack.

They fought back

In July 1919, white veterans were galvanized by a rumor that the Metropolitan Police Department in Washington, D.C., had released a black man suspected of sexually assaulting a white woman.

The men poured into black neighborhoods carrying pipes and lumber they found along the way, Rawn James Jr. writes in the History News Network.

"Thousands of white veterans in uniform snatched black people from streetcars, sidewalks and beat them without reason or mercy. Black women cried in the streets for God to save them," James writes.

In this 1919 photo provided by Chicago History Museum, a crowd of men and armed National Guard stand in front of the Ogden Cafe during race riots in Chicago.

But just like they had begun doing across the country, African Americans fought back. They too , began snatching white drivers out of vehicles or firing from their own cars. One black teenaged girl shot and killed a police officer.

"There were pockets of resistance (by African Americans)," Krugler says. "And that's another reason why the backlash was so harsh."

Further south, in Longview, Texas, where 31% of the population was black, African-American leaders were calling on black farmers to sell directly to buyers in Galveston and avoid going through white cotton brokers, the Texas State Historical Association reports.

One of the two black leaders, Samuel L. Jones, was assaulted and beaten in July and a day later, 12 white men tried to enter his house. They were met with gunfire and one of them was beaten by a group of black men.

They returned with more guns and ammunition, found the house empty, and set it on fire, along with other black residences.

In this July 13, 1919 image provided by the Library of Congress, Daniel Hoskins stands with guns deposited at Gregg County Courthouse, in Longview, Texas, following race riots during Red Summer.

In September, in Omaha, Nebraska, a mob stormed into a courthouse and dragged out a black man who had been accused of assaulting a white girl. The Omaha Bee reported that a " black beast " had assaulted the girl, according to History Nebraska, formerly Nebraska State Historical Society.

The man, Will Brown, was beaten, repeatedly shot and lynched.

"In its alliance with Tom Dennison, Omaha's powerful political boss, the Omaha Bee was the primary strident voice of alleged racially shocking crimes," the state society reported.

"Alarmed at the Bee's promotion of violence and racial prejudice, the Rev. John A. Williams—first president of the local chapter of the NAACP and publisher of the Monitor, a weekly black paper—called upon the editors of the Bee and the Daily News to stop their propaganda."

Blacks across the country set up armed self-defense patrols to protect the communities the police failed to protect, Krugler says.

But they weren't just fighting against the violence. They were fighting what Krugler calls a "three-front race war."

They were also fighting back against false media reports that blacks were the ones inciting violence and also fought for justice in biased courts.

"We see parallels to today," Krugler says. "We see African Americans continue all three of those fights into the 20th century and even the 21st century."

200 dead in Arkansas

One of the deadliest tragedies of Red Summer was in Elaine, Arkansas.

"By the end of the summer, every city was just waiting for theirs to happen, it was just all a giant panic," McWhirter says.

On September 30, as sharecroppers met to unionize against low wages, law enforcement officers drove by at night and claimed their car broke down. Soon, shots were fired.

It's still not clear who fired first, but white men used the rumors of an uprising to crush the sharecroppers' resistance. Hundreds of white men flocked from surrounding cities and states.

In the days that followed, white mobs swarmed the streets armed with rifles and more than 500 soldiers arrived to deal with "alleged black insurrectionists," the University of Arkansas Little Rock Center for Arkansas History and Culture says.

When blacks began running toward the troops to surrender, they were shot and killed.

The military reported about 20 African American deaths at the time, the university says. Similar estimates were given by local papers.

Today, the riots are known as the "Elaine Massacre" and one of the bloodiest racial conflicts in the nation.

An estimated 200 black people were killed by white people, according to Arkansas State Archives and the Equal Justice Initiative , an Alabama-based nonprofit that provides legal representation for indigent defendants.

Another 200 were jailed or put in stockades and many were tortured.

A grand jury charged 122 African Americans with crimes connected to the riots and a jury convicted 12 of them for murder, the government reports. They were later released with the help of the NAACP, according to the state archives.

The start of a movement

When Hartfield, the granddaughter of a woman who lived through the riots, began presenting around Chicago following the publication of her book, "A Few Red Drops: The Chicago Race Riot of 1919," she said she was surprised at how many people were unfamiliar with the state's history.

"It's about uncovering and commemorating something that's very tragic and ownership of something that really didn't go well," she said.

In this July 10, 2019, photo, a wreath lies in front of a site commemorating the 1919 race riots in Chicago.

It's a history the nation needs to build upon and learn from, she says.

There were seeds back then, she said, of issues American society is still grappling with today. Issues like racial inequality in the job market, the distrust between the blacks and the criminal justice system and biased news outlets.

"But I have hope," she says.