The severe weakening between 2008 and 2011 of the Islamic State of Iraq (ISI), the name al-Qa`ida in Iraq (AQI) had given itself in 2006, provides lessons for the current campaign against its successor, the Islamic State. The key to the earlier success was the United States’ ability to win the support of Sunni Arab tribes. This dynamic has proven more difcult to achieve today for a variety of reasons, including a lack of U.S. troops on the ground to temper discord and distrust between Shi`a-dominated Baghdad and the Sunnis as well as the decision not to confront Assad militarily in Syria. In addition, the Islamic State has been much more successful in monopolizing power in its core area than AQI/ISI ever was. Nevertheless, the most important reason for the eventual Sunni backlash against ISI—its brutal attempt to dominate Sunnis—is a dynamic still present in areas under Islamic State control today, providing an opportunity for the coalition to shrink the Sunni support base on which the group depends. But the radicalization of a generation by war and Islamic State brainwashing means that unless the underlying root causes of Sunni disenfranchisement are addressed and even if the Islamic State is defeated militarily in the coming months and years, the group could reemerge in new forms.