"The Afghan War:Last Nail in the Soviet Coffin"
Charlie Wilson's War is an enormously entertaining and informative history of the secret war that put the final nail in the Soviet coffin, leaving behind a vacuum into which stepped the Taliban and Al Queda. This is a truly great narrative of how we arrived in this post Cold War world with it's new terrorist wars.
(Another great book that addresses some of the same questions is, "All the Shah's Men" by Stephen Kinzer)