A short,, thoughtful article by Alireza Doostdar, an Assistant Professor of Islamic Studies and the Anthropology of Religion at the University of Chicago Divinity School:https://divinity.uchicago.edu/sighti...ireza-doostdar

A few passages:
We see ISIS as a unitary entity because ISIS propagandists want us to see it that way. This is why it is problematic to rely on doctrines espoused in propaganda to explain ISIS’ behavior....Focusing on doctrinal statements would have us homogenizing the entirety of ISIS’ military force as fighters motivated by an austere and virulent form of Salafi Islam. This is how ISIS wants us to see things, and it is often the view propagated by mainstream media.... But ISIS emerged from the fires of war, occupation, killing, torture, and disenfranchisement. It did not need to sell its doctrine to win recruits. It needed above all to prove itself effective against its foes.