A Shiite resurgence in Iraq has generated a region-wide Sunni backlash, raising fears of an emerging sectarian rift that is colouring and aggravating local conflicts. After discussing the schism’s origins, manifestations and implications, the author concludes that the primary battle in the region is not between Sunnis and Shiites but between the United States and Iran. A US–Iranian rapprochement would do much to reduce sectarian tensions, while the most effective long-term response to sectarianism itself will likely come from systemic restraints that exist in the form of countervailing loyalties that prevent any single allegiance, such as religious adherence, from becoming paramount.