The sesquicentennial of the Emancipation Proclamation’s signing is one reason to look back at the uphill battle of the movement to end slavery in the United States; Steven Spielberg’s hit film “Lincoln” is another.

But in fact, the movement’s significance to our history, both in the 19th century and well into modern times, makes it a worthy subject for the three-part “American Experience” documentary launching Jan. 8 on PBS.

“The Abolitionists,” written and directed by Rob Rapley, is a barely adequate documentary blending archival images with minimally convincing re-enactments. Fortunately, the content outweighs the weakness of the filmmaking itself.

Rapley’s film focuses some of the movement’s key members, including author Harriet Beecher Stowe, radical activist John Brown, former slave Frederick Douglass, South Carolina belle Angelina Grimk – who broke with her slave-owning family – and William Lloyd Garrison, who created the anti-slavery newspaper, The Liberator.

By 1820, there were some 2 million slaves in the U.S., and slavery was known as “the peculiar institution.” As the abolition movement grew as a human-rights battle, it became not just about slavery, but about race as well. However, eradication of slavery ran up against an even more powerful cultural opponent – economics – and not just in the South, but in the North as well.

The abolitionist movement was both organized, through the American Anti-Slavery Society, and unrelenting. Yet its leaders often disagreed on the best method to rid the nation of slavery. Garrison advocated peace and persuasion, or, as Brown termed it, “milk and water abolitionism.” Brown, the leader of the raid on Harper’s Ferry, motivated by the murder of an abolitionist in Illinois to believe that slavery could only be ended through bloodshed.

Setbacks to the movement such as the Great Compromise and the passage of the Fugitive Slave Law, as well as the Supreme Court’s decision on the Dred Scott Case that Congress could not outlaw slavery, radicalized even Garrison at one point. Over time, he came to believe the entire nation needed to start over, that the first republic had to die to create that “more perfect union” Lincoln would cite in his most famous speech.

Rapley’s film shows how much abolitionist leaders both worked together and disagreed while still keeping a collective eye on the prize. It also disabuses us of the notion that Lincoln was the great white hope of the abolitionist movement from the get-go. Like much of the nation, his views on slavery had to “evolve.”