"Jim Crow laws did not originate in the South; they originated in the North," Blight says.
The lesson: Don't reduce the issue of slavery to racism. Follow the money.
No. 3: Flawed reformers
The historian Henry Louis Gates Jr. once said that black abolitionists used to say that the only thing white abolitionists hated more than slavery was the slave.
"The Abolitionists" reveals that some of the most courageous anti-slavery activists were infected with the same white supremacist attitudes they crusaded against. White supremacy was so ingrained in early America that very few escaped its taint, even the most noble.
The documentary shows how racial tensions destroyed the friendship between two of the most famous abolitionists: Frederick Douglass and William Lloyd Garrison. Garrison was the editor of an abolitionist newspaper who convinced Douglass that he could be a leading spokesman against the institution that once held him captive.
Erica Armstrong Dunbar, a history professor featured in the film, says some abolitionists were uncomfortable with interracial relationships. They wouldn't walk with black acquaintances in public during the day, and refused to sit with them in church.
Lesson: Racism was so embedded in 19th century America that even those who fought against racism were unaware that it still had a hold on them.
"The majority of abolitionists did not believe in civic equality for blacks," Dunbar says. "They believed the institution of slavery was immoral, but questions about whether blacks were equal, let alone deserved the right to vote, were an entirely different subject."
No. 4: Lincoln the "recovering racist"
Tell some historians that "Lincoln freed the slaves" and one can virtually see the smoke come out of their ears.
"Please don't get me started," Dunbar says after hearing that phrase.
"There's this perception that good old Lincoln and a few others gave freedom to black people. The real story is that black people and people like Douglass wrestled their freedom away," Dunbar says.
Historians still argue over Lincoln's racial attitudes. The historian Henry Louis Gates Jr. once called him a "recovering racist" who used the N-word and liked black minstrel shows.
Others point to the public comments Lincoln made during one of his famed senatorial debates with Stephen Douglas in 1858 when he said, "There is a physical difference between the white and black races which I believe will forever forbid the two races living together on terms of social and political equality.
"There must be the position of superior and inferior, and I as much as any other man am in favor of having the superior position assigned to the white race," Lincoln said in the speech.
Spielberg's film depicts Lincoln as a resolute opponent of slavery, willing to deploy all the powers of his office to destroy it.
Yet "The Abolitionists" paints another portrait of Lincoln. It recounts how he supported colonization plans to ship willing slaves back to Africa. It says that Lincoln once floated a peace treaty offer to the Confederates that would allow them to keep slaves until 1900 if they surrendered. At one White House meeting with black ministers, Lincoln virtually blamed slaves for starting the war, the film's narrator says.
Blight, the Yale University historian, says Lincoln always personally hated slavery. He publicly spoke out against it as early as the 1840s, and spoke often about stopping the expansion of slavery.
Lincoln hoped to slowly end slavery without tearing the nation apart, Blight says.
"He was a gradualist," Blight says. "He was trying to prevent a bloody revolution over it. He couldn't."
He couldn't because of the pressure exerted by the abolitionists and the slaves themselves, other historians say. Blacks did not wait for white people to free them, they say. At least 180,000 blacks fought in the Civil War. And Douglass was one of Lincoln's harshest critics. He constantly pushed Lincoln to move aggressively against slavery.
The historian William Jelani Cobb wrote in a recent New Yorker essay on slavery:
"On the hundred-and-fiftieth anniversary of the Emancipation Proclamation, it's worth recalling that slavery was made unsustainable largely through the efforts of those who were enslaved. The record is replete with enslaved blacks---even so-called house slaves---who poisoned slaveholders, destroyed crops, 'accidentally' burned down buildings."
As for Lincoln's true feelings about blacks, that matter may always be subject to debate.