"To put it bluntly,

Islamic civilization died quite some time ago, unlike Islam which is very much alive; we will thus be concerned with the wider civilization only when it is relevant to features of the enduring religious heritage. The other reason is that a major component--perhaps the major component--of pre-modern Islam was Ṣūfism. Today Ṣūfism is by no means dead, but it is not at the cutting edge of the developments that concern us; instead its role is mainly that of a target for movements that see themselves as propagating pure Islam." 

-Michael Cook, Ancient Religions, Modern Politics, p. xiv.