Sanctions, embargoes, or isolationism are not going to help. Someone has to get blood on their hands. If their are locals ready to fight equip them to do it. A more certain solution would be a possibly apocalyptic one, and that is a no gain equation -- that might trigger the last war ...

What if; IS would just consolidate their holdings in the middle east and extort the oil price to over $200/barrel? Other oil exporters would just match the new market price.

Economic warfare with the rest of the world may be their end game too. There is more than one way to hand the world "heads in a bag." If this will be the case, a massive economic extortion: The last great recession that we are recovering from may be seen as a holiday picnic in retrospect.

Invasion is out of the question as there is no regular army to defeat. The local fighter ally will have a police action for years to control the Jihadists. So, there must be an organized local defense.

The Assad government has invited foreign military intervention to its assistance with ISIS in Syria but only with coordination with the Syrian government. The Syrians seem to think us foreigners need their permission even if Syria goes down the toilet alone with their false pride.

If no one does anything -- this will not turn out pretty. If we do take an interventionist position -- this will not turn out pretty. Either way, it is a lose - lose deal. So, which is the most palatable loss?