The movie's ultimate message is that honor, justice, and the American Constitution should always trump political expediency. Also, no matter how challenging a task might seem, you must rise up to it and have the courage of your own convictions.
Lincoln's assassination is shown in a harrowing sequence that unfolds in surprising detail. Blood is shown, but the actual wounds aren't. A connected attack is quite vicious -- a man stabs another who's lying helpless in bed, knifing him several times. John Wilkes Booth is shot dead. A hanging takes place in front of a crowd; it, too, plays out with agonizing specificity (including wince-inducing soud effects). Soldiers carry and use guns; the movie's opening shows dead/wounded men on a Civil War battlefield. A young woman is threatened; rocks are thrown through her window.
A couple kisses; some flirting.
Infrequent use of words like “damned," "hell," "oh my God," and "arse," plus a couple of uses of "s--t."
Some social drinking. A few characters use alcohol as "liquid courage" and take shots to fortify themselves before difficult tasks, and at one point, the main character turns to drink when all seems lost. One witness seems drunk in court. Era-accurate smoking, including during court proceedings.