In August 2003, at the age of thirty, Rory Stewart took a taxi from Jordan to Baghdad. A Farsi-speaking British diplomat who had recently completed an epic walk from Turkey to Bangladesh, he was soon appointed deputy governor of Amarah and then Nasiriyah, provinces in the remote, impoverished marsh regions of southern Iraq. He spent the next eleven months negotiating hostage releases, holding elections, and splicing together some semblance of an infrastructure...