With each day that passed after the 2003 invasion, the United States seemed to sink deeper in the treacherous quicksand of Iraq's social discord, floundering in the face of deep ethno-sectarian divisions that have impeded the creation of a viable state and the molding of a unified Iraqi identity. Yet as Adeed Dawisha shows in this superb political history, the story of a fragile and socially fractured Iraq did not begin with the invasion--it is as...