The 48 Laws of Power by Robert Greene and Joost Elffers. Where The Art of War, by Sun Tzu is written as an overview of the whole topic of strategy, seeking to provide an overall understanding of the subject; and The 36 Strategies tries to impart the knack of strategic thinking through 36 maxims related to well known Chinese folk stories, Mr. Greene focuses on how we influence and manipulate one another, ie "power".
Mr. Greene draws from both Eastern and Western history and literature as his source material. Sun Tzu and Machiavelli as cited as much as wonderful stories of famous con men. Among my favorites is about a scrap metal dealer thinking he bought the Eiffel Tower.
Each of the 48 Laws carries many examples, along with counter examples where it is appropriate that they be noted, and even reversals.
It is a very thorough study of the subject and the hardback version is beautifully produced.
Law #2: Never put too much trust in friends; learn to use your enemies.
Simply put, your friends like you, are well meaning and want to see that you benefit. They also have their own lives and concerns and will "get around" to doing what you ask of them, of looking out for you when it's convenient for them.
Enemies however, are committed. By learning to manipulate your enemies into action (or inaction), you can also spur your friends into action.