In my YA Fantasy, a military engagement is going to play a critical role about a third of the way through. There isn't much of this sort of thing in the story, but in this case it will be significant. I'm wondering if any of you know of some good resources for military strategy. Anything that deals with situations prior to modern warfare will be good. I have Sun Tzu's Art of War, and another books that details the particulars of a few battles, such as Agincourt. Nothing apart from Sun Tzu that speaks specifically to military strategy and theory, however. Any recommendations?