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It is a rare synchronicity when two fine and provocative movies based on true stories about national horrors – “12 Years a Slave” and “Dallas Buyers Club” – open at the same time. Not to equate the AIDS crisis with slavery, but to their victims, they were equally tragic and deadly.

Of the two, “12 Years a Slave” is much harder to watch. The horrors of “the peculiar institution” are portrayed graphically and at length.

The camera does not stint from the lash of the whip or the tightening of the noose. Slavery’s most egregious terrors – including abduction, rape, lynching, beating and murder perpetrated by loathsome plantation owners and evil slave masters – are unsparingly played out.

Only a few southerners are portrayed with an iota of decency. If this were a fictional movie, it would be derided as too dark and one-dimensional.

In fact, “12 Years a Slave” is based on the 1853 memoir of the same name, written by Solomon Northup, a free black man from upstate New York. While doing business in Washington, D.C., in 1841, Mr. Northup was kidnapped and sold to slave owners in Georgia.

His first owner, William Ford, played by Benedict Cumberbatch, admires Mr. Northup’s intelligence and skills. But when Mr. Northup threatens Mr. Ford’s slave master, he is sold to the sociopathic slave owner Edwin Epps.

 The movie has an excellent cast and a fine screenplay. The British-Nigerian actor Chiwetel Ejioforas as Mr. Northup and Michael Fassbender as the chilling Mr. Epps, who quotes scripture to justify his sadism and cruelty, are magnificent.

Smaller parts by Paul Giamatti, Brad Pitt and others are equally good. The scene in which the gospel singer Topsy Chapman leads the slaves in the spiritual Roll Jordan Roll, while Northup fights to restrain his emotions, is a classic. The film will doubtless be nominated for many Academy Awards.

“Dallas Buyers Club” tells the story of Ron Woodruff (Matthew McConaughey), who battles the FDA to bring unauthorized drugs to people with AIDS during the early days of the epidemic.

Mr. McConaughey lost 40 pounds to portray the gaunt, dying Woodruff. When he is first diagnosed, the doctor tells him he has 30 days to live.

But driven by a desire to take on the medical and legal establishments, he survives nine more years. “I’m fighting for life, and I ain’t got time to live,” he says ruefully, but his dedication helps other to live in the face of a terrifying disease and lack of sympathy or support from most doctors and regulators.

Mr. McConaughey is characteristically brilliant, bringing humor, intensity and nuance to the role of a man transformed from wild-living reprobate to conniving and passionate reformer. The musician Jared Leto plays Rayon, Woodruff’s transgender business partner, with great dignity and laconic grace.

Both movies are unsparing in depicting the painful suffering of their victims. But they should be required viewing for anyone who wants to bear witness to these tragedies and cares about perseverance, courage and redemption.