Two new books on Syria and ISIS

Charles R. Lister, The Syrian Jihad: Al-Qaeda, the Islamic State and the Evolution of an Insurgency.

Fawaz A. Gerges, ISIS: A History.

I have only browsed them, and I do not feel qualified to judge the details of the contents.  Nonetheless each seems more serious and better documented than the other extant writings on these topics which I have seen.