Steven Spielberg and this film's writer, Tony Kushner, have clearly done their research. Bar a few glaring anachronisms – one of the characters swearing as if he has just stepped in from the 21st century, for instance – the film is pretty much spot-on as a depiction of the circumstances surrounding Abraham Lincoln's pushing of the 13th amendment, to ban slavery, through the House of Representatives in 1865.

As Lincoln, Daniel Day-Lewis is excellent: he has the president's famous height, and his reedy, hushed manner of speaking. Apparently, Lincoln used to drive his colleagues mad with his odd sense of humour and his long stories, just as we see in the film. We also get a much more rounded picture than usual of Lincoln's wife, Mary Todd. She's notorious for being on the far side of sane – she's reputed to have thrown crockery at Lincoln – and for spending pots of money. Sally Field shows her as a much more complex person, who had suffered real loss in the death of their son Willie.

Unusually, for a film about the American civil war, the focus is on the fact that Lincoln believed that the southern states had never left the Union, despite having split away to form the Confederacy. He wanted the abolition of slavery to be a clear part of the constitution, followed by all the states in the Union, including those in the south. I have trouble explaining this to my students, but the film puts it across quite clearly. I'll definitely be using it as a teaching aid.

Lincoln is based on Doris Kearns Goodwin's 2005 biography Team of Rivals. That's an excellent book, but it's barely recognisable in this movie: Goodwin was primarily interested in Lincoln the politician; Spielberg's film is far more concerned with how slavery affected the civil war. Apparently, Team of Rivals is bedtime reading for Barack Obama.