Though to be a bit more serious about the ISIS claim of establishing a caliphate, one has to have a caliph that one would follow. Who is the one that anyone outside of ISIS true-believers would follow?

It also ignores that ISIS will barely be able to hold on to what territory they’ve claimed thus far.

As it is, the Iraqi government is continuing their pushback against ISIS advances, and it’s not likely that ISIS will be able to hold what they’ve taken.