The U.S. and coalition invasion of Iraq in spring 2003 has led to the most ambitious U.S. effort at nation-building since the end of World War II. Unlike the aftermath of World War II, however, the United States is faced with a ferocious insurgency that is threatening the emerging government of Iraq and its developing security forces. Moreover, this program of Iraqi political rehabilitation must be carried out in a part of the world that is well-known for its strong sensitivities about Western influence over that region. It must also be carried out without significant, in-country military support from the majority of U.S. allies, with the most important exception being the United Kingdom. Additionally, this transition must not only sweep aside an old society but build a new one based on the cooperation of Shi'ite Arabs, Sunni Arabs, Kurds, and other groups. Previous U.S. experience in coping with postwar problems has demonstrated that a military occupation resembles the major combat phase of a war in that both require maximum flexibility and adaptability on the part of military forces to meet consistently changing conditions. Moreover, past U.S. experience further illustrates that the population of a democratic country engaged in occupation duties can sometimes become first wary and then disillusioned as the enterprise continues into the indefinite future without clear and rapid progress. In the past, the United States has sometimes had to distinguish between optimal and acceptable end states in the countries being occupied, because the optimal end state is not always attainable, but worst case developments must still be prevented. These experiences are worthy of remembering as the United States struggles with the situation in Iraq.