Even with tearing apart a single book and turning it into three movies, Peter Jackson doesn't scratch the surface of J.R.R. Tolkien's rich lore.
The backstory to The Hobbit and the tale in The Lord of the Rings all take place in a mythology that isn't that deeply explored even in the books unless you crack open The Silmarillion. Since you likely don't have time to zip through that book before popping out to catch The Hobbit: Battle of the Five Armies, CGP Grey has just the video for you.
The famously insightful YouTuber does a delightful job of summarizing the basic mythology of the world, delivering some really interesting details that could help flesh out your experience watching the movies.