A review by archytas
Isis: A History by Fawaz A. Gerges

informative reflective medium-paced

3.5

"At the zenith of its power in 2001, the membership of bin Laden’s Al Qaeda was around one thousand fighters. In contrast, Baghdadi had a mini-army of between thirty thousand and one hundred thousand members controlling a de facto state roughly the size of the United Kingdom. By becoming the major beneficiary of the breakdown of state institutions in the Fertile Crescent, IS, together with like-minded Al Qaeda factions, was able to hijack people’s calls for freedom, justice, and dignity and turn popular as well as intellectual opinions against the Arab Spring uprisings."

This wasn't the easiest read: not so much the subject matter - Gerges avoids any gratutious descriptions of violence - but because the book has a semi-thematic, semi-chronological organising structure, which I found difficult to follow, and because it is a little ranty at times. I mean, you can forgive anyone being a bit ranty about ISIS, don't get me wrong. This is fundamentally (heh) a depressing story of two nations degenerating into repression and violence.
The book was substantially written before 2017, and then recently updated since the military defeats of ISIS. The new material is primarily in the introduction and the lengthy epilogue, and there are some strange inconsistencies as a result (Abu Bakr al Baghdadi's tense jumps around). But Gerges' analysis holds up, so mostly it works.
This analysis is largely that ISIS' distinguishing features were its willingness to use violence against Muslims, it's oppositional focus on the Shi'a, its attempts to form a Caliphate - even without state power - and the use of flamboyant cruelty, such as beheadings. It's success was a combination of these things - the idealism of the Caliphate mixed with a ruthless willingness to murder/eliminate all internal opponents or ideological alternatives - combined with a focus on recruiting working and destitute Sunni peoples. He argues that many in Syria and Mosul supported ISIS simply because they fixed power and water, and established civil services when these had been long abandoned. This wasn't necessarily what I expected from accounts I've read of survivors from Raqqa and other occupied cities, which have indicated that terror was ever present living under ISIS, but experiences change over time, so this may have been more so in the early days.
Or the other issue may be that most of what I have read is written by women, and women are remarkably absent from this narrative. Gerges rarely - quite possibly never - mentions gender. But the reality is that ISIS fighters, who make up the bulk of the supporters he discusses, were overwhelmingly male, and the women who joined ISIS had very different experiences. This felt like a big gap in the book, and I would suggest that readers think of supplementing this with Azedah Moaveni's Guest House for Young Widows, for example. 
But despite those complaints, this is a thorough look at ISIS and the personalities who created and maintained it, and is particularly strong in examining the relationship between Al Qaeda and ISIS.