Mazarr begins with the pundit George Will’s assessment that the decision to invade Iraq in 2003 was “worse than Vietnam, and the worst in American history.” Yet, he notes, we still don’t know when or how the decision to go to war was made: our understanding of why this catastrophe took place is “radically incomplete.” His attempt to close the gaps puts a great deal of the story into one thoroughly researched and eminently readable volume. Mazarr attributes the decision to invade to a characteristically American “missionary impulse” combined with “intuitive, value-driven judgment.” That’s a polite way of saying that the war was conceived by men and women who, although not evil, were so sure in their convictions regarding a country about which they knew hardly anything that they excused themselves from rigorous thought about what they were doing and why they were doing it and indulged in egregious distortions of the facts regarding Iraq’s weapons programs. It’s not obvious that there are lessons in this sorry tale that will help avoid a repetition of those blunders and misdeeds. Ironically, Mazarr himself is unable to pinpoint when and how the decision to go to war was made. But his story is an important one, and well told.