With “12 Years a Slave” sure to win at least a few Oscars on Sunday night, on the heels of the success of “Django Unchained” and “Lincoln,” stories of black slavery and black freedom seem to have definitively arrived in Hollywood.

I’m a great admirer of “12 Years,” having taught Solomon Northup’s narrative, the basis for the film, in my introduction to African-American history class for over 10 years. As pleased as I am to see such a searing and faithful historical treatment get its due on the big screen, however, so far as the history of slavery is concerned, the half has yet to be told.

If you’ve seen the movie, you might have thought that Northup’s experience of kidnapping and enslavement as a free black man in the north was a historical outlier. But it was far from unique.

New York City itself was a center of the shanghaiing of free blacks into slavery. A notorious gang known as the “black-birders,” in which some city policemen actively participated, at times with the connivance of local judicial authorities, regularly waylaid black men, women and children and sold them off to slavery in the antebellum period. Unlike Northup, some of them had no legal recourse, as they had been judicially remanded into slavery as suspected fugitive slaves....