Vintage photos of the Osage Nation, the tribe at the center of 'Killers of the Flower Moon'

• Martin Scorsese's film "Killers of the Flower Moon" is about a string of murders in 1920s Oklahoma.
• At the center of the conspiracy was the Osage Nation, a Native American tribe living in the state.
• Here's what the real Osage Nation looked like a century ago.

The Osage Nation is a Midwestern Native American tribe that originally developed in the Ohio and Mississippi valleys around 700 BC.

After getting forcibly displaced from their original territory in Kansas by the US government, the Osage people found a new home in Oklahoma during the 1800s.

In 1894, the Osage discovered the land they'd been given was oil-rich. It was so oil-rich, in fact, that the Osage became the richest people per capita in the world.

"In 1923 alone, the tribe took in more than $30 million, the equivalent today of more than $400 million," David Grann wrote in his 2017 book, "Killers of the Flower Moon."

The movie of the same name, starring Robert De Niro and Leonardo DiCaprio, follows the grisly history of what came next: a wide-ranging conspiracy of white Oklahomans who murdered dozens (if not more) Osage tribe members to gain control of their land.

Here's what the real members of the Osage Nation looked like before and during what became known as the "Reign of Terror."