Islamic State are not terrorists they employ terror as a tactic. You cannot bomb an idea, unless you are completely ruthless. It is true the liquidation of the radicals in the storming of the Paris Commune lobotomized the French working class movements in 1871, setting back the aroused citizens decades, but it is extremely difficult to wipe out an idea by killing everyone who thinks it, contrary to the imperial leaders of Washington strategies.
Of course those who have adopted the mantle of the Islamic Caliphate do so with some hubris. The last caliphate was the Abbasid ending in the 16th century. Sunni's believe the Caliph should be elected.
It is ironic that the US trains and arms insurgencies in other countries and then goes in to kill the very people they trained and armed.