British General Lord Richards, recently retired as their Chief of Defence Staff, is widely reported as noting that ISIS is not just a terrorist organisation, it also fields large conventional forces. As such, it will require conventional forces to defeat it. Further, in his view, these will certainly need to include ground forces - airstrikes on their own will not be sufficient (particularly those confined to within the borders of Iraq.
Unpalatable as it may sound, in the opinion of this senior army officer of 42 years military experience, the only way that ISIS can be defeated (let alone destroyed) is for the West to commit itself to an all-out war in the Middle East. According to Richards, an alliance with Russia would be necessary, as would the need to carry military operations across the border into Syria (there would be little likelihood of success if ISIS can take sanctuary in a neighbouring country).
Lord Richard's views are being widely reported at the moment (both in our Australian newspapers, and others). He may well have a point!