It's compelling, I want to see it again.
I'm pretty sure you'll be like me, you'll learn more about the 13th Amendment to the Constitution than you ever knew.
The amendment is surprisingly concise:
Section 1. Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.
Section 2. Congress shall have power to enforce this article by appropriate legislation.
It was speedily endorsed by the states and was finally approved on December 6, 1865, when Georgia ratified it.
It was the first step of Lincoln's plan for "reconstruction" of the South after the Civil War. Too bad he never had the chance to implement the rest of his program, which would have been considerably more reasonable than the harsh and careless policies adopted by the Radical Republicans after the assassination.
A side note about the movie: Wow, it was dark at night in 1865. Gas lamps and candles don't throw much light. It was shadowy indoors after sunset, and, to our modern sensibilities, gloomy. A little creepy…