Often artists themselves can't tell you why they gather around a theme at a certain moment in time.

This is one of those moments. And for whatever reason - the economic crisis, global tensions over immigration, a desire to ponder nationhood - America's history of slavery and racism is getting a thorough going over.

Last year two very different Oscar-nominated films dealt with slavery - Steven Spielberg's worthy Lincoln and Quentin Tarantino's comic-book Django Unchained; later in the year The Butler examined America's civil rights history. Ironically, all three are now outshone by a film by a British director, albeit one with a very clear and personal reason for engaging with the subject, namely his own family's experience of slavery.

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Steve McQueen's 12 Years A Slave is an exceptional, overwhelming film, which depicts with integrity and artistry what one character aptly describes as the "fearful ill" that beset America. It will leave you shaken, saddened, but ultimately moved to the good.

A pre-Civil war story, it is based on the memoir of a free man from upstate New York who in 1841 was kidnapped and sold into slavery in the South. In a prelude that becomes more poignant as the story unfolds, we see Solomon Northup (Chiwetel Ejiofor) enjoying his independence. An accomplished musician, he has a home, a family and a place in society. But then this big-hearted man is duped, drugged, chained and shipped to Louisiana for a very different life.

Over the next 12 years Solomon will have a handful of owners, ranging from the inherently decent Ford (Benedict Cumberbatch), who struggles with his role as a slave owner, to the sadistic Edwin Epps (Michael Fassbender), who has no such misgivings, quoting scripture to justify the savage beating of his slaves.

If physical and mental abuse and virtual imprisonment are not bad enough, the proud and intelligent Northup has to forsake his identity - to accept the new name forced upon him, to suppress his education - in order to survive. He suffers all the more because of what he has lost. And as he angrily tells a fellow slave: "I don't wanna survive, I wanna live."

Compared to McQueen's previous films, Hunger and Shame, the narrative style is straightforward, even conventional, the director understanding that this story needs no embellishment, no ­interpretation, that the raw telling of it will cut us to the quick. Scenes in which Northup and other slaves are beaten make anger rise in your throat; when he is left hanging from a tree, only his toes saving him from death, McQueen holds the moment so long that it is almost unbearable. The fate of a female slave (Lupita Nyong'o), who has the misfortune to attract Epps's twisted affections, is heartbreaking.

Rather than the gleeful gratuitousness Tarantino employed in Django Unchained, there is cool reason to this assault on our senses, a desire to be true to the complex emotional responses of both black and white characters to the barbarity of the time. The gorgeous imagery does not sweeten the pill so much as remind us of the disjunction between this natural idyll and the behaviour within it.

Ejiofor's performance is all the more towering for its understatement. The actor conveys a myriad of emotions, often at once and without dialogue, chief of which are a dignity and humanity that the film needs in the face of such unfathomable cruelty. He's well supported, notably by Fassbender, the director's favourite actor, whose Epps is at once bloodcurdling and pathetic, and Brad Pitt, whose cameo literally raises the spirits.