Donald Trump makes his first appearance in Ava DuVernay’s Oscar-nominated documentary 13th around the halfway mark, as he posts his notorious full-page ad in the New York Times calling for the death penalty for the Central Park Five in 1989. But he comes back with a bang at the end of the film, which was released in October 2016, at a time when Trump was widely thought to have blown his presidential bid. “In the good old days,” he roars to his all-white crowd, as DuVernay builds a montage of civil rights workers being fire-hosed and black men being beaten in the streets, “they would have carried ’em out on a stretcher!”

13th review: Ava DuVernay doc shows prisons are the new plantations Read more

Cutting back and forth from historical footage of lynchings, Emmett Till’s brutally beaten face and 1980s drug raids to images of punch-ups and racial taunting at Trump rallies, DuVernay links our dire present to America’s racist past. It vividly demonstrates that history can go backwards as well as forwards. “That is a big statement,” she says, “but I’d also say that there’s something possible here in terms of empathy that is beautiful and that might not have been there before. All of a sudden you have all this marching – huge airport demonstrations, the Women’s March – and it’s an activation for a whole lot of people who weren’t affected by this before, because none of it touched their lives, they’d never felt any kind of oppression or threat to their humanity.”

DuVernay is always on the lookout for hope, even in times as dark as ours. Serious as she is about her subject, in person she exudes endless warmth and good humour. Her documentary takes a single clause in the 13th amendment to the US constitution – the one that freed the slaves – and detects therein a template for all future oppression of America’s black and brown peoples. The amendment’s first section reads: “Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.”

Facebook Twitter Pinterest Donald Trump during a campaign rally in Warren, Michigan, March 2016. Photograph: Carlos Barria/Reuters

That bulky midsection became the basis for the new slavery of post-reconstruction Jim Crow laws. Slavery was at heart an economic, labour-centric phenomenon, so, once it was abolished, the midsection offered a get-out clause that was eagerly embraced by mostly southern states in need of cheap labour. It’s simple: shift the laws to make more criminals, then make them work for free as prisoners. Slavery resurrected under another name. As prison reform activist and ex-con Glenn E Martin tells DuVernay: “Every time you give me liberty, the handcuffs come out right after.” If this sounds arcane, note that Victoria’s Secret was only recently shamed out of using prison labour to make its products.

Facebook Twitter Pinterest Political activist and academic Angela Davis in a scene from 13th. Photograph: Netflix/AP

The film really gains steam during the post-civil rights era, as it shows successive presidents – Nixon, Reagan, Clinton – making seismic adjustments in crime and punishment (and in public perceptions) that substantially affect African-American lives. J Edgar Hoover criminalising black dissent, and even, in the case of people such as Angela Davis, criminalising black intellectual thought; the shifting of legal goalposts in Reagan’s war on drugs through to California’s three-strikes law and Clinton’s 1994 federal crime bill, which together quadrupled the national prison population and started a massive privatised prison-building programme (raising the need for more prisoners to make more profit). And from Trayvon Martin and Eric Garner to Ferguson and Trump, DuVernay weaves a web that, as she says, “crosses entire generations and affects entire communities”. At its core is, as one of her many witnesses calls it, “a prison-industrial complex that eats black and Latino people for breakfast, lunch and dinner”.

Facebook Twitter Pinterest A demonstration led by activist Quanell X (right) in 2013, in Houston, over the death of Trayvon Martin. Photograph: Eric Kayne/AP

“Inherent in this 13th amendment that is supposed to propagate freedom,” DuVernay says, “there is a shackle. Both within the amendment and in the way it’s structured, and the way it’s been used, there is a big story about black people in this country, and the durable systems that have been labelled as one thing but actually do another, and that’s what the 13th is about.”

And DuVernay is well placed to tell it. Her own life intersects with a volatile era in race relations in Los Angeles. Born in Compton and raised under the post-Watts riots, all-white rule of Daryl Gates’s LAPD, she was 20 years old and studying film at UCLA when the 1992 Rodney King uprising took place, and working as a CBS Evening News intern during the OJ Trial – “going through the OJ jurors’ garbage cans”, she chuckles.

“I grew up in Compton, with a very heavy police presence, a lot of arrests around me, a lot of police aggression, a lot of issues of crime and punishment and justice. Any kind of sense of justice or dignity I have was formed in that period. We grew up with Daryl Gates’s LAPD, we lived under the “Ghetto Bird” – the chopper always circling overhead, shining lights in our house. Really formative times, with lots of militant activism and consciousness-raising.”

DuVernay attended UCLA, then a beacon for young black filmmakers because of the LA Rebellion film movement that had flourished on campus in the 70s and 80s, producing directors such as Haile Gerima, Charles Burnett and Julie Dash.

“I wrote for the black student newspaper, was in the African Student Union, and I started to learn about black liberation theory – that the freedom of black peoples around the world has been a great threat to the systems that profit from us. And then becoming a filmmaker and tackling those issues through more intimate stories like Middle of Nowhere, my film about a woman whose husband is incarcerated, and then Queen Sugar, my TV series that has a formerly incarcerated father at its centre. Incarceration and its results are something I feel passionately about.”

Facebook Twitter Pinterest Omari Hardwick and Emayatzy Corinealdi in Middle of Nowhere. Photograph: Allstar/Kandoo Films

Does she think 13th will help Americans face up to the legacy of slavery? “The sad truth,” she says with despondency, “is that some minds just will not be changed. It might help all of us to once in a while get outside of the United States itself, like go to South Africa or Germany. Because inherent in the very cultural fabric there, you have a sense of the past and of reckoning with it, saying, ‘This happened, and we will bear witness and we will learn from it, we will speak it and say that it happened and we will remember it.’ And we don’t do that here, so we can’t even have a real conversation about it. Because we have not been taught to talk to each other, and we have not been taught to remember.”

13th is available on Netflix.