Heads in the Sand: How the Republicans Screw Up Foreign Policy and Foreign Policy Screws Up the Democrats by Matthew Yglesias
This is a great introduction into how the Iraq War got started, and shed a lot on what has been going on in the States to an outsider, but there is a danger of seeing the UK's action as simply the result of US domestic politics. What role did UK hawks and doves have in the lead up to and during the Iraq War?
This book is hard going on the atheist. Without belief in the first principles of Christianity - that the bible is the work of God, rather than a socially constructed text, then most of the arguments fall flat.

