The Art of War 

This is the definitive work on the strategy of conflict. Written by Sun Tzu over 2000 years ago, this book is neither dated or vague in any way. It is taught in business schools from Harvard to Osaka. What is so interesting is that the author is so against war: "To win without fighting is the best." This is also required reading for any martial artist, I prefer the translation by Thomas Cleary.  He adds comments by famous martial artists and generals from then until now. Sun Tzu says it best," If you  know yourself and you know your enemy, you need not fear the result of a hundred battles. If you know yourself and know not your enemy, for every victory gained you will also suffer a defeat. If you know not yourself nor your enemy, you will surely succomb in every encounter."