PRINCETON, N.J. — The Arab world has entered the most dramatic period in its modern history. Oppressive regimes are being swept away, as Arab people finally take their fate into their own hands.

The excitement of the moment, however, does not tell us what the future holds. At best, democracy is still off in the distance: The military still dominates in Egypt and Tunisia, tribal forces are on the rise in Libya and Yemen, and sectarian divides between Sunni and Shiites are likely to dominate politics in Bahrain, as they have in Iraq since 2003.

There is no single narrative that makes sense of this all. Regimes throughout the Middle East, the United States and European governments, as well as al-Qaida and other Islamist groups, are all struggling to understand what comes next.