Shadi Hamid offers his take on what attracts people to ISIS, and why that attraction is specific to Islam:
ISIS draws on, and draws strength from, ideas that have broad resonance among Muslim-majority populations. They may not agree with ISIS’s interpretation of the caliphate, but the notion of a caliphate—the historical political entity governed by Islamic law and tradition—is a powerful one, even among more secular-minded Muslims. The caliphate, something that hasn’t existed since 1924, is a reminder of how one of the world’s great civilizations endured one of the more precipitous declines in human history. The gap between what Muslims once were and where they now find themselves is at the center of the anger and humiliation that drive political violence in the Middle East. But there is also a sense of loss and longing for an organic legal and political order that succeeded for centuries before its slow but decisive dismantling. Ever since, Muslims, and particularly Arab Muslims, have been struggling to define the contours of an appropriate post-caliphate political model.
In contrast, the early Christian community, as Princeton historian Michael Cook notes, “lacked a conception of an intrinsically Christian state” and was willing to coexist with and even recognize Roman law. For this reason, among others, the equivalent of ISIS simply couldn’t exist in Christian-majority societies. Neither would the pragmatic, mainstream Islamist movements that oppose ISIS and its idiosyncratic, totalitarian take on the Islamic polity. While they have little in common with Islamist extremists, in both means and ends, the Muslim Brotherhood and its many descendants and affiliates do have a particular vision for society that puts Islam and Islamic law at the center of public life. The vast majority of Western Christians—including committed conservatives—cannot conceive of a comprehensive legal-social order anchored by religion. However, the vast majority of, say, Egyptians and Jordanians can and do.