It generally does not work. ISIS is being financed by major donors in the middle east. There are so many deceitful people who smile at the west and make statements they they are against ISIS .....BUT ..... the truth is they are themselves financing and helping ISIS in many ways! The US is also playing a game and could do much more to destroy roads, oil wells smugglers to defeat them.
At least initially, a few of the powerful royal family members in Saudi Arabia and Qatar were supporting the ISIS. But now, this inflow seems to have slowed down. The main focus of the Arab Sheikhs have shifted to the Al Nusra front, the Ahrar ash Sham and the other "moderate" terrorists. Now ISIS is generating income on its own, by selling oil, extortion, dacoity.etc.