The sultans who created the Ottoman Empire - the most powerful Muslim state and the most extensive caliphate in history - did not base their rule on Shariah alone. As mentioned, they established a body of common law, Kanun, that paralleled the religious law of Shariah.A book about Sufism, tracing it from beginning to the present day, linking together various things of which I was aware and in which I was already interested (the Bektashi, Rūmī, the whirling dervishes, Said Nursî) into a longer historical narrative.
Unfortunately it's not all that good. to start with it's a work of apologetics written by a true believer, viewing events and people jumbled together through a partisan lens. A lot of effort is spent on denouncing Wahhabism (fair enough, but that then means you don't let your own people stand on their own merits). The net of historical adherents to Sufism is cast rather with, including some people who I suspect had never heard of it in reality. The narrative is curiously unmoored from the wider historical context. the explanation of Sufist ideas seemed relatively clear, but I was irritated by the failure to link it convincingly to other things I know about. I'm sure there are better books about Sufism out there, and I'll keep an eye out for them.
This was the non-fiction book that had lingered longest on my unread shelves since I got it in 2010 (sent by the author I think). Next on that list is 1688: A Global History by John E. Wills.