“I don’t have a right to make movies,” Warwick Thornton says, bluntly. You might expect a director fresh from a buzzing festival circuit and with sales in every single international market to be a little more self-congratulatory. But Thornton, like his new film, has more important things on his mind.

“The screen should never be abused by a writer or a director – if I get access to that screen, it needs to be something important to say,” he says. When the script for Sweet Country landed in front of him, he knew it was a story worth telling. “It made me angry, it made me happy, it made me sad, it made me cry, it made me proud,” he says.

The finished film makes every second count. Part road movie, western and legal drama, it follows Aboriginal stockman Sam Kelly (played by Hamilton Morris) as he is reluctantly drawn into white Australia’s criminal justice system after the death of a pastoralist and ex-serviceman (played by Ewen Leslie). Drawn from true events, it explores a side of Australia’s frontier history rarely shown on screen.

“It’s amazing how much Australia doesn’t know about itself,” Thornton says. “This idea that we were created through this utopia, where everything was perfect – what happened to history? Why don’t we learn this in our curriculum? Why is it 2018 and I’m making a movie about it? There is seriously a problem with our history. It’s embarrassing.”

To draw audiences into that world of 1920s central Australia, Thornton embraces and subverts the genre trappings of the western. The wide-brimmed hats and ochre-colour palettes are familiar, but moralities are blurred, the politics of the frontier are reframed – there’s certainly no familiar Morricone-inspired score whistling over the lingering shots of salt lakes, red dirt and scrub.

“We’re more intelligent than that,” Thornton says of the absence of a conventional soundtrack, which he describes as “a key to cry to”. “A lot of directors abuse the score, I’m not an anti-score person but for this film I didn’t want it. I wanted it to be truthful to the time and the place. If you were standing there in 1929, there wasn’t a score, there wasn’t a violin.”

Like Samson and Delilah, the new film is both disarmingly sweet and jarringly painful; made all the more potent by the uncomfortable truths at its heart. Staples of white Australia’s identity, from the hardworking but virtuous settler to our love of the fair go, are exposed as fragile myths. They’re replaced by an affecting insight into the erasure of culture and connection to country typically ignored by mainstream Australia.

Those things had a comprehensive influence on Thornton’s process, from casting the film to surrendering to the rhythms of the country while making it. “It’s incredibly important,” he says of casting non-professional actors from the local Arrernte community around Alice Springs. “I can teach people to act but I can’t teach them to be Aboriginal, that’s just the way it is. If I’m making a film about the Arrernte, I’m casting the Arrernte. They have a connection I can’t teach.”

Then there’s the land itself. “The country is a character, it needs its own time and place, and when you’re out there in reality you start working to the timing of the country – you don’t walk in and use a city attitude in the desert. We changed the attitude through the editing, and the timings and the sound because the desert’s dictating how you make a movie. That was really important, to recognise it as a character and use it as a character – and it’s a very empowering thing.”

Released at the height of the annual debate surrounding January 26, Sweet Country is shockingly relevant. It’s hard to avoid drawing parallels between onscreen townsfolk sprawled out on a pub veranda shouting slurs at Kelly’s open-air trial to the racially fuelled messages posted to Facebook “community” groups and pages today; where death and violence are seen as just responses to minor or imagined crimes.

“What’s changed?” Thornton asks. “Except now it’s faceless and from behind a computer rather than a bloke on a horse chasing down a black man who you’ve decided is guilty. So a young man walking through town, and then on Facebook someone reporting there’s a black man walking through town, is exactly the same shit. It’s just happening today.

“Australia needs films like this to give it a reality check. We can make another Ned Kelly movie, but I don’t think that’s gonna help anything.”

Sweet Country is in cinemas nationally.