It should be kept in mind that a primary objective of the US, and of multinational corporations as well, is social and political destabilization. Instability in the society and in political structures marginalizes the population and creates ideal conditions for predatory corporate domination. Generally, where the potential profits are greater, the methods of destabilization will be proportionately more severe. This is the explanation for ISIS’ existence.
While it is clear that ISIS achieved its seizure of Mosul with the support of the Muslims who have been terribly antagonized by the extremist sectarian policies of Al-Maliki, this does not mean that ISIS has their best interests in mind.
It is plausible, and has been articulated by both US and Israeli policy advisers, that the West’s objective in the region is the redividing of Syria and Iraq into a set of smaller states. There is nothing in ISIS’ actions which contradict this supposition, indeed, the taking of Mosul, and the leaving of Kurdish areas, only supports the theory.