Here’s a timeline of Tulsa’s past:

1830: The Indian Removal Act is signed by President Andrew Jackson, pushing 60,000 Native Americans, including the Cherokee, Creek, Seminole, Choctaw and Chickasaw, off their lands in the southeast United States. The Native Americans are forced by federal troops to walk hundreds of miles to what is now Oklahoma. Historians say more than 15,000 died of exposure, starvation and exhaustion on what is known as the Trail of Tears.

1834: Indian Territory is established by Congress in what would become Oklahoma.

1882: Tulsa becomes a stop on the St. Louis and San Francisco Railroad.

1887: Congress passes the Dawes Act, which divides up Indian lands in Oklahoma into individual plots.

1890: The Oklahoma Territorial Act is approved by Congress, establishing Oklahoma as a U.S. territory.

1898: Congress passes the Curtis Act, which limits the authority of Native American governments and allows land allotted individually to Native Americans to be sold to white settlers. A land rush begins with more than 50,000 lining up to claim a piece of what the federal government calls “unassigned lands in Oklahoma Territory.”

Jan. 18, 1898: Tulsa is incorporated as a city.

1901: Oil is discovered in Tulsa.

1906: The Greenwood district is established by O.W. Gurley, a Black entrepreneur who moves to Tulsa and buys 40 acres of land “to be sold to Coloreds only.” He becomes known as the founder of Black Wall Street.

Nov. 16, 1907: Oklahoma is admitted to the Union as the nation’s 46th state.

Dec. 4, 1907: The Oklahoma State Legislature passes oppressive Jim Crow laws, establishing strict segregation of whites and blacks.

1915: Black businessman Simon Berry establishes Greenwood’s first public transportation system, “Berry’s Jitney Service,” and a charter airplane service.

May 30, 1921: A 19-year-old Black shoe shiner is arrested for allegedly assaulting a white woman in downtown Tulsa. A white mob gathers outside the Tulsa County Courthouse, where he’s being held. Dozens of Black men, including World War I veterans, rush to the courthouse to protect him. A struggle ensues. A shot is fired. Then hundreds of white people march on the Greenwood district in a murderous rage, leading to one of the worst episodes of racial violence in U.S. history.

May 31, 1921: The mob sets fire to hundreds of black-owned businesses and homes. Historians believe as many as 300 black people were killed and more than 10,000 black residents were left homeless. Witnesses report they saw planes dropping kerosene bombs from the sky and bodies loaded onto trucks.

June 1, 1921: With the Greenwood district mostly destroyed, martial law is declared and thousands of Black residents are rounded up and held at the city’s fairgrounds and other locations until a white person vouches for them.

For decades afterward, few white people would talk about what happened. Black survivors spoke about the race massacre in whispers. Thousands of people who lost their homes and businesses in the fires were never compensated, though many rebuilt anyway. No one was arrested.

1957: Tulsa takes its first halting steps to desegregate its schools in the wake of the landmark Supreme Court decision in Brown vs. the Board of Education. Little progress is made.

1968: The U.S. Justice Department files suit against the Tulsa public school system to force it to desegregate.

1972: Tulsa establishes a magnet program, busing students from the all-Black Booker T. Washington High School to white high schools.

1970s: Much of Greenwood’s historic commercial center is demolished to make way for Interstate 244.

1997: The Tulsa Race Riot Commission is formed to research what happened during the race massacre. Survivors describe harrowing scenes of death and destruction, including bodies being tossed into mass graves.

1999: Renowned forensic anthropologist Clyde Snow discovers evidence of a mass grave using ground-penetrating radar.

2001: The Tulsa Race Riot Commission issues its final report, recommending the city dig for possible mass graves and pay reparations to survivors and descendants of survivors. Neither happens.

2005: The U.S. Supreme Court refuses to hear a case filed by race massacre survivors seeking reparations.

2010: John Hope Franklin Reconciliation Park opens, detailing Tulsa’s violent racial history.

2011: The Oklahoma legislature mandates that the massacre be taught in public schools, but attaches no funding to develop a curriculum.

Sept. 28, 2018: The Washington Post publishes a front-page article about the unresolved questions about the rampage, prompting Tulsa’s Republican mayor, G.T. Bynum, to reopen the investigation into whether there are mass graves.

Oct. 20, 2019: HBO’s acclaimed series “Watchmen” opens with scenes of a race massacre in Tulsa.

Oct. 23, 2019: Tulsa begins searching again for evidence of mass graves, with scientists, including forensic anthropologists, using ground-penetrating radar at Oaklawn Cemetery.

Dec. 15, 2019: The team of forensic scientists, archaeologists and anthropologists announces it has discovered “anomalies” consistent with mass graves at two sites that warrant further examination.

Feb. 3, 2020: Tulsa announces it plans to dig for suspected mass graves in Oaklawn Cemetery, but delays the excavation because of the coronavirus pandemic.

June 10, 2020: President Trump announces he will hold a political rally in Tulsa, the site of a race massacre, on Juneteenth, a holiday celebrating an end to slavery. After an outcry from African Americans, he delays the rally by one day.