My response: You seem to think of ISIS as a nation-state because it has established caliphates, occupying areas within countries; it is not. ISIS has evolved into a transnational guerilla movement.
Where possible, ISIS still tries to establish cells, but today their members are bound more by their extremist ideology than by traditional borders.
ISIS also inspires “lone wolf” sympathizers. These people, usually better educated and including converts who are not of Arab origin, are inspired by ISIS’ rhetoric to commit terrorist attacks. Some of these lone wolves are directed, however peripherally, by ISIS interlocutors(1), but most seem to have been radicalized through the internet and act out of sympathy to ISIS’ extremism.
ISIS cannot be defeated by means of sanctions. A coordinated effort that cuts off financial support, addresses the hopelessness of its youngest converts, and marginalizes the group by exerting pressure from within the Arab world is more likely to bring an end to ISIS.