Seeing the topics you mention, I am thinking that the sci-fi book Ender's Game written by Orsson Scott Card is going to be perfect for you. There's war topics in it, strategy, it's a fairly light, shortish book. And from there, you have a whole series of books if you do enjoy it. But be warned, do not watch the movie.
When I read that book, I got hooked and couldn't drop it until I finished it.