As of October 5, 201 black people had been killed by law enforcement officers in the United States in 2016 alone. The circumstances leading to their deaths varied greatly. The reasons, generally, did not.

Filmmaker Ava DuVernay, who directed the Academy Award-nominated Selma, explores these reasons in 13th, a powerful 200-minute documentary that premieres on Netflix Friday. The film tells the story of how white, wealthy and politically-powerful Americans responded to the abolition of slavery in 1865 by creating new forms of bondage for black people — and encoding them through a racist criminal justice system.

These forms of bondage included, but were not limited to, aggressive incarceration and its fallout, including parole. The film argues these systems are maintained today through racially asymmetrical law enforcement practices — including racial profiling by police and, more recently, mandatory minimumjail sentences for nonviolent drug offenses.

By the film’s conclusion, DuVernay demonstrates that racism under the law may be a hot-button topic of discussion today, but it’s also part of a centuries-old tale that still hasn’t been told enough — and, perhaps, won’t ever be fully told.

“The whole film is about callbacks to history and knowing that this present moment isn’t isolated,” DuVernay, who spoke to small groups of journalists gathered in a suite at the JW Marriott Essex Hotel in Manhattan, said Saturday. “It’s part of a legacy, an insidious, violent legacy, that’s generations old.”