The problem is not ISIS itself . If the money is good you will always find nutters who will want to play war . And its not just the nutters that will join , the hopeless and unenployed will also pick up the gun . So the suply of arms is unlimited if the money is right and the target is a destabilised area .
Fisrt kill the money supply , the USA's greatest ally , Saudi Arabia . Its just a joke what that backwards savage country gets away with . ISIS suply , Yemen , 9/11 , building moschees around the word and promoting radicalism , just to name a few .
After that kill off the 'internal' money supply (oil) and cripple the marketing department . Its a joke again , for example Twitter , bans Milo for a movie review (not politicaly correct) but lets daesh savages post beheadings .
After this is all done i think you dont need any more intervention , let the local power , backed by its people deal with them .
The main problem is not isis , the main question is who is benefitting from all this ? Why can saudi arabia do what it does ? Why is Assad suddenly a bad tirant after he choose a alternative gas pipe ?
Purge the ones that put money and power above lives and call the shots .
The problem is there is no power who could do this .