The stealthy and morally dubious process of politics is part of the narrative of a hit movie, “Lincoln,” as the wartime president in what would come to be his last months on earth wheedled lawmakers into passage of the 13th Amendment to the U.S. Constitution.

If that political emphasis, by screenwriter and Louisiana native Tony Kushner, shocks some viewers raised on a nobler account of events, it is nevertheless a reminder of how much compromise, half-measures and political prevarication was needed 150 years ago to deal with the endemic racism of most of the American people.

Those who envisioned complete freedom for black Americans, most of them slaves in the Southern states, were few. Very few indeed, and most Americans could not comprehend the idea of emancipation; pre-war abolitionists were often stoned by mobs, and the emerging Republican Party dealt gingerly with its opposition to slavery. Lincoln himself promoted the foolish notion of sending America’s slaves back to Africa en masse.

But as the movie demonstrates, while he had become a liberator, Lincoln was still a canny politician. And that quality, or drawback depending on your view, was particularly emphasized by the Emancipation Proclamation, officially issued on New Years Day 150 years ago.

The slaves were freed on the basis of military necessity, in areas of rebellion. The president knew he did not have the authority to do more, and — as he already had in the first two years of war in other ways — stretched presidential powers to the limit.

In some places, emancipation was already a fact: South Carolina commemorated the events of that New Year's proclamation because the Sea Island slaves already had been freed by Union Army landings earlier in the war. New Orleans was a Union outpost by then, although its curious amalgam of races and cultures had made the transition perhaps less dramatic there than in rural areas.

Wherever it was read, though, the proclamation was understood: Freedom once obtained was impossible to live without. The right to learn to read and write alone was undreamed of, even for pious slave families who had memorized large tracts of Bible verse in oral traditions.

As the Union forces advanced, large tracts of the slave states would become subject to the Emancipation Proclamation. It was to be months, until after the titanic struggle at Gettysburg, before Lincoln gave the speech that promised “a new birth of freedom” for Americans, regardless of the color of their skin.

Yet behind the political phrases of the proclamation was a great cause that people felt in the deepest parts of their souls.