Manisha Sinha is a professor of Afro-American studies and history at the University of Massachusetts, Amherst. She is the author of “The Counterrevolution of Slavery: Politics and Ideology in Antebellum South Carolina” and the forthcoming “The Slave’s Cause: Abolition and the Origins of America’s Interracial Democracy.”

On the 150th anniversary of the Emancipation Proclamation, discussion over who freed the slaves, fueled by movies like “Lincoln,” have become commonplace. While historians have debated the relative roles of Abraham Lincoln and the slaves themselves in the coming of emancipation, few have paid attention to the abolitionists, the forgotten emancipationists in the story of black freedom.

Actually, they’re hidden in plain sight, even in contemporary emancipation narratives. In Steven Spielberg’s “Lincoln,” which may well win the Academy Award for Best Picture this evening, they are represented by the lone figure of the Radical Republican Congressman Thaddeus Stevens. In Quentin Tarantino’s fictional western on slavery, “Django Unchained,” perhaps by the articulate German bounty hunter posing as a dentist (Christoph Waltz’s character isn’t pure fantasy; many “Forty Eighters,” refugees from the failed 1848 revolution in the German states, were political radicals and staunchly antislavery). In fact, the idea of a Thirteenth Amendment to the Constitution abolishing slavery, the subject of Lincoln, originated with abolitionists.

The problem with movies like “Lincoln” is not that they depict passive black characters — in fact most black characters in the movie are drawn in a nuanced fashion — but that nearly all characters in the movie, including Lincoln himself, are devoid of their proper historical context, particularly the abolitionists and the even larger political antislavery movements. Emancipation was not simply a presidential and congressional game; it was the long and hard-won result of decades of black and white activism before and during the war....