In his scathing rebuff of the film Lincoln (which I also hated, for some similar but less precise reasons) Aaron Bady argues it was the blacks themselves to a far greater extent than the film acknowledges:
In short, if you widen your field of view, you will discover that W.E.B. Du Bois argued a century ago—and as the historical scholarship has increasingly come to agree—that slavery was already all but dead by the time Lincoln got around to declaring himself an abolitionist, far less because the North gave slaves their legal freedom than because they had already effectively taken it, because it had become the new status quo that would have required force to dislodge. At the end of the Civil War, with the South defeated, the choice for the north was not to end slavery or leave it; the choice was to ratify the fact that it was already dead or to re-impose it by military force.
In short, the idea that the white north “gave” freedom to the slaves draws from and reinforces an attractively simple and flattering myth, one which formed around the old historiography of the period like a noose cutting off oxygen to the brain: the myth that black slaves were rendered passive by their condition, and that—absent an outside force interrupting their state of un-freedom—they would simply have continued, as slaves, indefinitely. It’s only in this narrative that freedom can be a thing which is given to them: because they are essentially passive and inert, they require someone else—say, a great emancipator—to step in and raise them up.
W.E.B. Du Bois was already chipping away at this myth in 1909, but when scholars in the post-Civil Rights era started taking him and his 1935 Black Reconstruction seriously, the historiographic mainstream turned this myth on its head. Slaves were not and could not be “given” their freedom because they had always had it: it had required a great deal of violent force and political work to keep them enslaved, and when that force was removed—as the South collapsed politically and militarily—they began to act like the human beings they always already were, organizing, moving, and seizing their destinies in their own hands. At this point, the game was up; just as the institution of slavery had always depended on substantial governmental enforcement and support, it would have taken a substantial amount of violent force to re-impose it, a concerted project to re-establish slavery that no one in the north had any particular stomach for. At the end of the Civil War, to put it simply, the North had a simple choice: re-imposing slavery by force or accept the new reality. They chose the latter.
If you read these books, however, you’d gain a sense of perspective that the film works to make impossible. Spielberg and Kushner are interested in a kind of scrupulous (almost farcical) accuracy about things that do not matter, while working very hard to place everything else that was going on in the period—and everything else Lincoln was responding to—off camera. “The nation’s capital was transformed by the migration of fugitive slaves from the South during the war, but you’d never know it from this film,” as Kate Masur points out, and Lincoln’s own servants were leaders and organizers in this community, something of which Lincoln simply could not have been unaware. But the film makes a point of not showing any of this: while the vast majority of the movie takes place in cramped and smoky rooms, even the exterior shots (usually of conversations in moving wagons) show us very little of what was going on in the streets and neighborhoods of Washington (much less what was going on in the South). Which is to say: they give us the illusion of perspective without giving us its substance. They show you the elephant’s tail quite accurately, and then they declare, on that basis, that the entire beast is a snake.