The revolutions and revolts in the Arab world, playing out in just a few months across two continents, have proved so inspirational to so many because they offer a new sense of national identity built on the idea of citizenship. But in the past weeks, the spectre of divisions—religion in Egypt, fundamentalism in Tunisia, sect in Syria and Bahrain, clan in Libya—has threatened uprisings that once seemed to promise to resolve questions that have vexed the Arab world since the era of colonialism.