It's important to keep in mind that these are non-state players. ISIS or ISIL, if you will, is not a country. Conventional military operations don't very much apply. They have no capitol to capture, no infrastructure of their own, no territory of their own. This is unconventional warfare in the raw. The need to to "attrit" their leadership, as they say in the Pentagon. Kill or capture ( preferably kill) their leadership, when new leaders take over, they move up on the hit parade. How is this to be done? ISIS has enemies. So in addition to drone strikes, air strikes and all the rest, it's important to play one group against the other. Some of that is going on now, It's risky. You may replace ISIS with something as bad or worse, but it doesn't require much in the way of troop commitments and that is critical in the U.S. with our current political climate.