My cover story in The Atlantic’s March issue asked, as simply as possible, What does ISIS believe, and what are its ideological roots? I read every ISIS statement I could find, including fatwas and tweets and road signs, and I front-loaded my mornings with execution videos in hopes that by bedtime I’d have forgotten enough of the imagery to sleep without nightmares. I picked through every spoken or written word in search of signals of what ISIS cares about and how its members justify their violence. I also asked a small group of its most doctrinaire overseas supporters for guidance, and they obliged.

At the time, the dominant cliché about ISIS was that it was a thrill-kill group that had hijacked Islam for its own ends, and that these ends were cynical, pathological, and secular. The investigation yielded something like the opposite conclusion: ISIS had hijacked secular sources of power and grievance, and was using them for religious ends—ends that are, at least among some supporters, sincere and carefully thought through. They include a belief in the imminent fulfillment of prophecy, with the group in a key role.

I am grateful for thoughtful reaction from many sources. (I’ll examine separately the pushback to my claim that ISIS is within the Islamic tradition.) Shadi Hamid of the Brookings Institution emphasized that ideology is deeply embedded in social and political facts, and that ignoring those facts is at least as dangerous as ignoring the ideology. I agree completely: ISIS achieved its successes in a hellish setting where all authority was predatory and nothing was safe; it offered certainty, sincerity, and the promise of reliability; it did this in ways that were antithetical to traditional interpretations of Islam (though not quite as antithetical as some believe).

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, 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.

Anjem Choudary, the notorious London blowhard who patiently explained the version of jihadism he supports, tweeted the story out, pleased that he and his minions got their airtime. Musa Cerantonio, a more soft-spoken and scholarly young Australian who did the same, sent a long and thoughtful email with a few points of correction and clarification. He stressed that execution for wearing Western clothes and shaving is not an Islamic State practice. I think he’s right. ISIS certainly forbids shaving, but merely to commit a sin is not grounds for excommunication or killing. (To excommunicate over matters of sin would put the Islamic State in line with the Kharijites, an early sect to which ISIS’s Muslim enemies often compare the group.) He added that dying without pledging allegiance to a valid caliph, which I correctly quoted him as saying is “a death of disbelief,” is not to die as an infidel. He said that the quote as printed misleadingly left open the interpretation that he was calling Muslims infidels. To do so would jeopardize his own status as a Muslim.

But the most interesting comments concerned my story’s popularity among ISIS supporters (referred to below with the shorthand "Muslims"). I was unsurprised to see it shared online by Islamic State fans, at least somewhat positively, but of course I was still uncomfortable about being praised by avowed génocidaires. One ISIS supporter wrote to me to note the peculiarity in all this. The piece, he said,

is grounded in realism, and argues that not understanding what is happening is very dangerous, especially if fighting a war, one must fight the war that is real, not the invented one that one wishes to fight. Perhaps ironically, your [writings] ... are most dangerous to the Muslims (not that it is necessarily meant to be so on your behalf), yet they are celebrated by Muslims who see them as pieces that speak the truth that so many try to deny, but also because [Muslims] know that deep down the idealists of the world will still ignore them.

What stands out to me that others don't seem to discuss much, is how the Islamic State, Osama [bin Laden] and others are operating as if they are reading from a script that was written 1,400 years ago. They not only follow these prophecies, but plan ahead based upon them. One would therefore assume that the enemies of Islam would note this and prepare adequately, but [it’s] almost as if they feel that playing along would mean that they believe in the prophecies too, and so they ignore them and go about things their own way. ... [The] enemies of the Muslims may be aware of what the Muslims are planning, but it won't benefit them at all as they prefer to either keep their heads in the sand, or to fight their imaginary war based upon rational freedom-loving democrats vs. irrational evil terrorist madmen. With this in mind, maybe you can understand to some degree one of the reasons why many Muslims will share your piece. It’s not because we don't understand what it is saying in terms of how to defeat the Muslims, rather it’s because we know that those in charge will ignore it and screw things up anyway.