I suggested that religious ideology was underrated as an explanatory lens—indeed, barely understood as one—but didn’t specify the relative importance of it versus other factors, specifically “the bad governance, the shifting social mores, the humiliation of living in lands valued only for their oil.” If I could specify that relative importance, I would; I find the confidence of others in this regard fascinating. But as I wrote in the original essay: “Without acknowledgment of these factors, no explanation of the rise of the Islamic State could be complete.” I set out to write an essay about this group’s ideology, which heretofore has gone underacknowledged, so I don’t apologize for doing just that, though I take to heart Hamid’s counsel to see these elements as less separable than they appear.

J.M. Berger, also of Brookings, argued that the religiosity of the group matters less than its importance as an identity movement, an aggressive form of defining membership in a group. I’d add that the type of religious ideology ISIS espouses is remarkably well-adapted for brutal enforcement of group membership. This type of jihadi-Salafism, unapologetically aimed at purifying Islam through killing, was obsessively policing its adherents well before the rise of the Islamic State. Understanding that sect is a way to understand its associated identity.

Andrew Anderson, who studies jihadists, wrote this fine reflection on the context of the Islamic State's views of warfare, which he places in the medieval period rather than in the early Islamic conquests to which ISIS considers its project the rightful heir. He and my colleague Frank Griffel at Yale both point out how ISIS, which is so keen to emphasize its early-Islamic cred, differs from early Islam in important and substantive ways.

For an Islamist perspective, I’d refer you to http://justpaste.it/jhxc, a quick reply by a Twitter user who rebuked me gently (thanks) for missteps and ended with a proposal I dearly hope comes to pass. “What is really needed,” he wrote, “is a delegation from an ‘Islamist’ background to visit Islamic State territory and engage with their leadership and ideologues as well as their common fighters.” He doubted that the specific ideologues I met are the best representatives of the group’s ideology. “Until that happens it is hard to truly fathom what this movement is about and what it truly wants.”

As for the reaction from the Islamic State: I noticed my article tweeted out multiple times by ISIS supporters, at least once by a fan of the group who noted nervously that the guy who wrote it must be spying on their tweets. Those whose comments I saw were delighted that I had taken their ideology seriously and concluded that ISIS is an Islamic group. Their delight pleases me only because my intention was to describe the group in terms it recognized and considered fair. I suppose at least some supporters thought I succeeded, or at least came closer than the last infidel who tried.