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.

Mr. Ricks's narrative is based on hundreds of interviews and more than 37,000 pages of documents, and many of the book's most scorching assessments of the White House and Pentagon's conduct of the war come from members of the uniformed military and official military reports.

An after-action review from the Third Infantry Division underscores the Pentagon's paucity of postwar planning, stating that "there was no guidance for restoring order in Baghdad, creating an interim government, hiring government and essential services employees, and ensuring that the judicial system was operational." And an end-of-tour report by a colonel assigned to the Coalition Provisional Authority memorably summarized his office's work as "pasting feathers together, hoping for a duck."

Mr. Ricks writes in these pages as both a reporter and an analyst, and many of his findings amplify observations made by other journalists and former insiders in earlier books: namely that the Bush White House routinely ignored the advice of experts (be they military, diplomatic or Middle East experts); that Defense Secretary Donald H. Rumsfeld's determination to conduct the war with a light, fast force had crippling consequences for the American military's ability to restore law and order in post-invasion Iraq; and that infighting between the State and Defense Departments, between civilians at the Pentagon and the uniformed military, and between the military and the Coalition Provisional Authority severely hampered the making and execution of United States policy.

"Fiasco" does not possess the dramatic combat details of "Cobra II" by Michael R. Gordon (chief military correspondent for The New York Times) and Bernard E. Trainor (a retired Marine Corps lieutenant general and former military correspondent for The Times), but unlike that book, which basically ends in the summer of 2003, it goes on to chronicle America's flailing efforts to contain a metastasizing insurgency over the next three years.

Mr. Ricks argues that the invasion of Iraq "was based on perhaps the worst war plan in American history," an incomplete plan that "confused removing Iraq's regime with the far more difficult task of changing the entire country." The result of going in with too few troops and no larger strategic plan, he says, was "that the U.S. effort resembled a banana republic coup d'état more than a full-scale war plan that reflected the ambition of a great power to alter the politics of a crucial region of the world."

This was partly a byproduct of the Pollyannaish optimism of hawks like Deputy Defense Secretary Paul D. Wolfowitz, who slapped down the estimate by the Army's chief of staff, Gen. Eric K. Shinseki, that several hundred thousand soldiers would be required to secure Iraq. And it was partly a byproduct of a conviction shared by Secretary Rumsfeld and Gen. Tommy Franks that speed, in Mr. Ricks's words, "could be substituted for mass in military operations."

Mr. Rumsfeld's stubborn reluctance to acknowledge a growing insurgency and his resistance to making adjustments, Mr. Ricks says, contributed further to the military's problems on the ground. A continuing shortage of troops meant that borders could not be sealed, armament caches could not be secured, and security and basic services could not be restored. As a consequence support for the occupation rapidly dwindled among the Iraqis.

To make matters worse, Mr. Ricks adds, the Army seemed to have "forgotten almost everything it had learned in the Vietnam War about counterinsurgency." During 2003 and much of 2004 effective counterinsurgency measures aimed at winning the political support of the Iraqi people were not being employed; instead, an emphasis was put on "the use of force, on powerful retaliation and on protecting U.S. troops at all costs."

There were mass roundups of Iraqis (many of them bystanders caught up in the sweeps), and some of those detainees were harshly treated by American troops who had not been "trained or mentally prepared for the mission" they faced in postwar Iraq. Mr. Ricks sees the Abu Ghraib scandal not as an anomalous incident but as "the logical and predictable outcome of a series of panicky decisions made by senior commanders, which in turn had resulted from the divided, troop-poor approach devised months earlier by Secretary Rumsfeld and Gen. Franks."

Mr. Ricks notes that the Bush administration has tended "to dismiss critics as ‘Monday morning quarterbacks,' " but he points out that that phrase "conveniently disregarded the fact that many of the critics had expressed their worries before the war even began." His book is replete with warnings from Middle East experts and military veterans (like Gen. Anthony C. Zinni and Gen. H. Norman Schwarzkopf), who presciently cautioned that the invasion and its aftermath would not be as simple or as fast as many in the administration predicted.

In late 2002, Mr. Ricks reports, 70 national security experts and Mideast scholars met at the National Defense University to discuss the looming war and concluded that occupying Iraq would "be the most daunting and complex task the U.S. and the international community will have undertaken since the end of World War II." The group's emphasis on the importance of "maintaining a secure environment" in post-invasion Iraq and its recommendation against a swift dissolution of the Iraqi military would be ignored in the ensuing months.

"It isn't clear that a large and persistent insurgency was inevitable," Mr. Ricks concludes, adding that "the U.S. approach, both in occupation policy and military tactics, helped spur the insurgency and made it broader than it might have been." Among the crucial post-invasion missteps made by the Bush administration, he suggests, were the decision, after the fall of Baghdad, not to send two additional divisions of troops immediately, which might have helped keep the lid on the insurgency, and the orders issued by the head of the American occupation, L. Paul Bremer III, disbanding the old Iraqi army and banning thousands of Baath Party officials from returning to their government jobs.

The failure to contain the insurgency would have dire consequences as the war dragged on. While the occupation of Iraq (which Mr. Wolfowitz had predicted would basically pay for itself through oil revenue) was costing American taxpayers an estimated $5 billion a month in 2004 and 2005, the chaos-ridden country was replacing Afghanistan as a training ground for a new generation of terrorists. Meanwhile, writes Mr. Ricks, the United States Army found itself in a strategic position that "painfully resembled that of the Soviet Union in Afghanistan in the early 1980's."

Not only had the war "stressed the U.S. Army to the breaking point," a study published by the Army War College's Strategic Studies Institute declared, but it had also turned out to be "an unnecessary preventive war of choice" that "created a new front in the Middle East for Islamic terrorism and diverted attention and resources away from securing the American homeland" against further attacks from Al Qaeda. The war "was not integral" to the global war on terrorism, the report concluded, but was a costly "detour from it."

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