In the larger scheme of things, though, it's clear that sectarian polarization is a genuine and intensifying trend. Roy sees only two scenarios that might derail it. Reform of the revolutionary regime in Iran could theoretically moderate Tehran's role in fomenting Shiite activism abroad. And collapse of the Assad regime, followed by a "smooth transition in Syria," would deprive the Iranians of one of their most important regional partners and cut them off from access to their Hezbollah allies in Lebanon, thus forcing them to scale back their ambitions. Needless to say, neither of these possibilities appears especially likely any time soon. So we're probably well-advised to expect the worst.