Disney would never actually make a movie about the Arthurian Legend that truly reflects reality. Henry Treece, however, is not Disney and he has written a brutal book about the rise of Britain the likes of which you have never read.
Not every book I read is non-fiction. In fact, some of the most thought provoking and life altering texts can come from novels. One such book: The Chrysalids. Honestly one of the best books I have ever read in the genre.