The Art of War: The Classic Text on the Conduct of Warfare is by Sun Tzu. This must read classic is not just about the principles of war, but the principles of life. It is an easy read and a short one, but don't let it's brevity deceive you - the ideas and philosophy it lays out are deep, rich, profound and not mined in one read. This is a Reader's Corner Highly Recommended book and one you must read before you die. It is rated 10th grade due to the depth of content even though it can be read by much lower readers.
Ratings: 10th grade - 10 out of 10.