Gen. David Petraeus is the subject of The Insurgents: David Petraeus and the Plot to Change the American Way of War, a new book by Fred Kaplan. Shah Marai/AFP/Getty Images hide caption

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President Obama nominates former Sen. Chuck Hagel, R-Neb., to be defense secretary Monday at the White House. Mark Wilson/Getty Images hide caption

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Marilyn Gonzalez (left) and her daughter, Jessica Pedraza, at their base in Kuwait in 2010. Courtesy of Jessica Pedraza hide caption

itoggle caption Courtesy of Jessica Pedraza

Ali, an Iraqi teenager, wears Spc. Justin Cliburn's helmet and radio equipment in Baghdad. Ali and Cliburn became unlikely friends while Cliburn trained Iraqi police in 2005 and 2006. Courtesy of Justin Cliburn hide caption

itoggle caption Courtesy of Justin Cliburn

A scene from the early days of the fighting in Iraq in the spring of 2003. In one incident, three members of an Iraqi family were killed. A U.S. Marine involved in the shooting recently tracked down the family to ask for forgiveness. Laurent Rebours/AP hide caption

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Sgt. Ben Roberts (center), recently returned from Afghanistan, speaks with Chick-fil-A manager Michael Sims at a military job fair in Columbia, S.C., in January. John Moore/Getty Images hide caption

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