The beginning of this book has a lot of useful information on the formation of ISIS. The authors present a lot of detailed information on Az-Zarqawi and Al-Qaeda in Iraq and how this ultimately led to the formation of ISIS. I think they did a a pretty good job describing how the power vacuum left by the US led invasion allowed Al-Qaeda in Iraq to flourish, which in turn, allowed ISIS to form. They also present a lot of useful information on how the advancement of Shi'a leaders at the cost of Sunnis led to the insurgency and ultimately, ISIS.

However, as the book went on it dragged. The book is pretty dry and I found it difficult to finish. The chapters that actually focus on ISIS as it is now were boring. The authors managed to interview a few ISIS members but what they said about their motivations is nothing new. If you've kept up with the news for the past year, nothing in the second half is enlightening.