I have come across no book that better explains the how and why off the world than Diplomacy. Its one of the few books I've ever found really worthwhile to read.
I really, strongly recommend you to read "The Prize", by Daniel Yergin. Won the Pulitzer. If you want to understand the world and how it works, and the REAL reasons for the History to be what it is, this is it. Best book in existence for Diplomacy, global economy and geopolitics. You will be amazed. You will never look at the world the same way again.