Fascinating article in The Nation by a researcher who interviewed ISIS fighters to find out what motivated them. I strongly suggest you read the whole thing:

More pertinent than Islamic theology is that there are other, much more convincing, explanations as to why they’ve fought for the side they did. At the end of the interview with the first prisoner we ask, “Do you have any questions for us?” For the first time since he came into the room he smiles—in surprise—and finally tells us what really motivated him, without any prompting. He knows there is an American in the room, and can perhaps guess, from his demeanor and his questions, that this American is ex-military, and directs his “question,” in the form of an enraged statement, straight at him. “The Americans came,” he said. “They took away Saddam, but they also took away our security. I didn’t like Saddam, we were starving then, but at least we didn’t have war. When you came here, the civil war started.”

ISIS is the first group since Al Qaeda to offer these young men a way to defend their dignity, family, and tribe.

This whole experience has been very familiar indeed to Doug Stone, the American general on the receiving end of this diatribe. “He fits the absolutely typical profile,” Stone said afterward. “The average age of all the prisoners in Iraq when I was here was 27; they were married; they had two children; had got to sixth to eighth grade. He has exactly the same profile as 80 percent of the prisoners then…and his number-one complaint about the security and against all American forces was the exact same complaint from every single detainee.”

These boys came of age under the disastrous American occupation after 2003, in the chaotic and violent Arab part of Iraq, ruled by the viciously sectarian Shia government of Nouri al-Maliki. Growing up Sunni Arab was no fun. A later interviewee described his life growing up under American occupation: He couldn’t go out, he didn’t have a life, and he specifically mentioned that he didn’t have girlfriends. An Islamic State fighter’s biggest resentment was the lack of an adolescence. Another of the interviewees was displaced at the critical age of 13, when his family fled to Kirkuk from Diyala province at the height of Iraq’s sectarian civil war. They are children of the occupation, many with missing fathers at crucial periods (through jail, death from execution, or fighting in the insurgency), filled with rage against America and their own government. They are not fueled by the idea of an Islamic caliphate without borders; rather, ISIS is the first group since the crushed Al Qaeda to offer these humiliated and enraged young men a way to defend their dignity, family, and tribe. This is not radicalization to the ISIS way of life, but the promise of a way out of their insecure and undignified lives; the promise of living in pride as Iraqi Sunni Arabs, which is not just a religious identity but cultural, tribal, and land-based, too.

An illustration of the less-than-total commitment to the cause of the Islamic State by Iraqis came from the Kurdish peshmerga Gen. Aziz Waysi, commander of the elite Zerevani (“Golden”) forces. He relates an overheard conversation between an ISIS fighter on the battleground and his leader, via a walkie-talkie previously confiscated from an ISIS corpse. “My brother is with me, but he is dead, and we are surrounded, we need help at least to take away my brother’s body,” General Waysi heard, and then the reply: “What else could you want? Your brother is in heaven and you are about to be.” This answer wasn’t what the poor surrounded young man was hoping for. “Please come and rescue me,” he said, “That heaven, I don’t want it.” But they didn’t, leaving him to whatever paradise awaited.