What is the ‘Islamic State’?

And of course we should read this alongside knowledge of how all 'states' were/are formed  and that the French, UK and US governments were murdering and looting, instilling fear in the population and living on stolen goods  from gangster-like  gangs long before ISIS appeared on the scene. 

I think here are significant differences to 'tradiotnal state formation', whilst primary accumulation (i.e. extraction of raw surplus) is an inherent part, most states emerge from within a wider culture, hence the formulation of 'selective inventive tradition', myth of the Norman Yolk not withstanding.  This is important, because most states have some element of buy-in from the local population, and as they develop, there is the element of the state as the terms of the class truce.With regard to Empire and Colonialism, don't forget that the European empires were outgrowths of free enetrprise, i.e. that there were classes of people outside the state who did the slave trading and primary accumulation (albeit with the backing of the state).IS aren't looking for buy-in, and their membersdon't have private enterprises (AFAICS) outside that organisation.  Their plundering is more akin to the Spanish Conquistadors, more direct and naked (and, thus, weaker).  IS is more akin to an imposed culture (and it hasn't been round long enough to see what sway the apparent allegiance of the tribes will have).

This might make interesting reading. Building a viable country rooted in fundamentalist theology was the central aim of ISIS. http://www.theguardian.com/world/2015/dec/07/leaked-isis-document-reveals-plan-building-state-syria

I didn't say social contract, but truce.  The US constitution contains the hidden hand of Shay's rebellion, the role of slaves who joined the British during the War of Independence, etc.  The British state contains laws demanded by the workers movement.  The US did conquer groups like the Navajo Empire, who were themselves busy expanding over other trabal groups (and remain the Native American Nation today: https://en.wikipedia.org/wiki/Indian_reservation).The idea of reservations shows the quasi truce like nature of legal systems, since these legal entities now shape a relationship that has underlying force.  As I recall, in many instances, the state in the US lagged behind the private enterprise of the settlers (indeed, in some senses, the British intention to recognise the Native Borders and stop expandsion was a proximate cause of the War of Independence).Agency is not a one way street. A 'selective invented tradition' means appropriation and recuperation of culture by the  hegemonic elite, but also implie that there is a dialogue and something like a common language.

More background info on the system of economic exploitation imposed by ISIS in the areas it controls:http://www.syriahr.com/en/2015/12/islamic-state-seizes-half-of-some-businessmens-money-in-the-countryside-of-deir-ezzor-and-it-covers-the-expenses-of-its-military-operations-from-collecting-zakat/Basically direct plundering to share out amongst its fighters, all under the guise of religion of course.