He points out how sectarianism has confounded foreign policy in places like Kosovo, Iraq, and Afghanistan, not to mention the Sudan, Libya, Mali, and Nigeria. For example, Rieff quotes Valli Nasr's essay for Foreign Affairs in 2006:
The Bush administration thought of politics as the relationship between individuals and the state, and so it failed to recognize that people in the Middle East see politics also as the balance of power among communities.Sectarianism is going on today in Syria and elsewhere, at gunpoint. However, don't limit sectarianism to the Middle East. Rieff gives the example of Belgium's two main ethnic groups: Flemish and Walloon. I'd add Canada's English and French speakers. I'm certain you have your own favorite examples.