The title of this devastating new book about the American war in Iraq says it all: “Fiasco.” That is the judgment that Thomas E. Ricks, senior Pentagon correspondent for The Washington Post, passes on the Bush administration’s decision to invade Iraq and its management of the war and the occupation. And he serves up his portrait of that war as a misguided exercise in hubris, incompetence and folly with a wealth of detail and evidence that is both staggeringly vivid and persuasive.

By virtue of the author’s wealth of sources within the American military and the book’s comprehensive timeline (beginning with the administration’s inflammatory statements about Saddam Hussein in the wake of 9/11, through the invasion and occupation, to the escalating religious and ethnic strife that afflicts the country today), “Fiasco” is absolutely essential reading for anyone interested in understanding how the United States came to go to war in Iraq, how a bungled occupation fed a ballooning insurgency and how these events will affect the future of the American military. Though other books have depicted aspects of the Iraq war in more intimate and harrowing detail, though other books have broken more news about aspects of the war, this volume gives the reader a lucid, tough-minded overview of this tragic enterprise that stands apart from earlier assessments in terms of simple coherence and scope.

“President George W. Bush’s decision to invade Iraq in 2003 ultimately may come to be seen as one of the most profligate actions in the history of American foreign policy,” Mr. Ricks writes. “The consequences of his choice won’t be clear for decades, but it already is abundantly apparent in mid-2006 that the U.S. government went to war in Iraq with scant solid international support and on the basis of incorrect information — about weapons of mass destruction and a supposed nexus between Saddam Hussein and Al Qaeda’s terrorism — and then occupied the country negligently. Thousands of U.S. troops and an untold number of Iraqis have died. Hundreds of billions of dollars have been spent, many of them squandered. Democracy may yet come to Iraq and the region, but so too may civil war or a regional conflagration, which in turn could lead to spiraling oil prices and a global economic shock.”

Much of the material dealing with the time just before the war has been chronicled in earlier books (not to mention an outpouring of newspaper and magazine articles), but Mr. Ricks provides a succinct narrative that emphasizes how this period “laid the shaky foundation for the derelict occupation that followed.” He reminds us that when it came to the threat posed by Mr. Hussein, the administration consistently emphasized “worst-case scenarios” even as it was “ ‘best-casing’ the subsequent cost and difficulty of occupying the country.” And he shows how this blinkered outlook resulted in a failure to plan for the realities of the occupation and a failure to allocate sufficient manpower and resources.