A current estimate is that this groups troop total has risen from about 10,000 up to 20,000 31,000. Plus the huge amount of military gear and finances they have. Such as the Syrian airfield and Iraqi army bases they captured full of war planes, tanks, humvees, missle trucks, helicopters...
Also reports are that they bring in over 2 million a day on the black market.
This group is not your average terrorist org. This is a whole new animal. This is a terrorist army. Troops on the ground will be needed to beat them. But they should be Syrian, Kurdish, Iraqi, Turkish, Iranian,Jordanian, Saudi...troops. Have America cover the skies and have other nations like Russia, Germany, France, Britian and China provide material support to their army of choice. Like Russia and China proping up the Syrian and Iranian armies. And France and Britian the Kurdish and Jordanian armies.