While the brutal injustice the film depicts is a cause for shame, it is "an even bigger disgrace that it takes a British director to stare the issue in its face", says Peter Debruge, of Variety magazine, one of the few American critics to note this tension at the heart of the production.
The film is adapted from the memoir of Solomon Northup, a black labourer and violinist living in New York in the mid-19th century. By 1841, Northup, born a free man after his father was emancipated in the will of his late owner, was living comfortably with his wife, Anne, and their three young children.
A bogus offer of lucrative work drew him to Washington DC, where he was drugged, kidnapped and shipped to Louisiana and sold for US$1,000 to a plantation owner played by Benedict Cumberbatch - another Briton.
Accused of lying whenever he protested with details of his true identity, Northup was renamed Platt, and put to back-breaking work in swampish heat with other slaves, who were among the millions of Africans taken from their countries and shipped to the New World.
A dispute led to Northup being sold on to Edwin Epps, a "repulsive and coarse" cotton-planter portrayed by Irish-German actor Michael Fassbender, who sadistically whipped his slaves "just for the pleasure of hearing them screech and scream, as the great welts were planted on their backs", Northup recalled in his book.
McQueen's depictions of Epps' beatings, more explicit than in any past Hollywood portrayal of slavery, are so excruciating that some American cinemagoers have walked out of screenings, unable to keep watching as Fassbender's bloody whip cracks into torn flesh.
"It is intense and it is raw, yet it is also beautifully human," said Dr Kellie Carter Jackson, a fellow at Harvard University's Department of African and African American Studies, who teaches a course on slavery in film. "I have yet to see another movie tackle slavery so well."
Northup's explosive account of his enslavement caused a sensation on its publication after he was freed in 1853, but his book fell into obscurity for more than 100 years, before being rediscovered and republished by two Louisiana academics amid the civil-rights battles of the 60s. But then it disappeared again.
Bianca Stigter, a historian and mother of McQueen's daughter, chanced upon the book as the couple searched for the right story of slavery to adapt for film.
"I could not believe that I had never heard of this book," McQueen writes in the foreword to a new edition. "It felt as important as Anne Frank's diary, only published nearly 100 years before."
While the story of the Holocaust's most famous victim has been used to educate millions of American children about the evils inflicted in Europe in the 40s, few would know about the ordeal of this 33-year-old caught up in their country's own moral outrage a century earlier.
"In America, looking at bad guys generally as Nazis is okay," McQueen said. "But when you're talking about home, you really don't want to be perceived as bad."
Two of the biggest Hollywood attempts to deal with the subject - Steven Spielberg's Amistad (1997) and Lincoln (2012) - focused on legal and political efforts by heroic white figures to save black slaves.
Even Roots, the landmark history by Alex Haley adapted for a hammy 12-hour US television mini-series in the 1970s, balked at showing quite the sort of merciless and sexual violence that is visited on slaves by Fassbender's Epps and his wife, Mary, played by Sarah Paulson.
Of course, the British Empire played a leading role in the business of humans-as-livestock.
McQueen, whose parents came to England from Grenada and Trinidad, says he owes his existence to ancestors who survived enslavement by British colonists. Ejiofor's forebears in the Nigerian Ibo tribe were among those plundered for the slave trade.
Yet McQueen, a Turner Prize-winning CBE, and Ejiofor, Royal Shakespeare Company actor, also look back at the era as members of the establishment of a country that outlawed slavery decades before Northup's ordeal, and whose shores were largely untainted by the shameful practices carried out in its name - an advantage unavailable to American filmmakers.
"America is yet to produce a film like this," said Dr Roderick Harrison, a sociologist specialising in race at Howard University.
"Americans have a great deal of difficulty because of their intimate proximity with slavery.
"Its true horrors have often been denied."
Despite last year's re-election of President Barack Obama reinforcing the view among some Europeans that racial tensions are practically a thing of America's past, sharper and more painful disparities persist between whites and African Americans.
White workers earn on average 30 per cent more than blacks, white American families have an average household wealth of US$110,729 ($133,838) - 22 times greater than the US$4,995 of the average black family - a gap that almost doubled during the last recession.
The gap between the proportion of white and black Americans earning university degrees is almost twice as large as it was in 1962, and while black people make up about 30 per cent of Americans, they are 60 per cent of the country's prison population.
"One of the biggest fallacies of the Obama presidency is that he has ushered in a post-racial society in which racism and discrimination are no longer problems," said Carter Jackson. "In fact, the systemic racism that is built in to the system and is very difficult to put your finger on or digest - that goes on."
British movie men
Steve McQueen:
• Who: British film director, screenwriter, and video artist
• Age: 44.
• Films: Deadpan, Hunger, Shame, 12 Years a Slave
•
Awards:
Camera d'Or at the Cannes Film Festival, a Turner Prize and a Bafta
Chiwetel Ejiofor:
• Who: British TV, theatre and film actor
• Age: 36.
• Films/TV: 12 Years a Slave, Children of Men, American Gangster, Salt, The Shadow Line
• Awards: Laurence Olivier Award for best actor, British Independent Film Award for best actor
