Many terrorist organizations in history have exploited the desire for the unity of Muslims, but the strong view on a caliphate is that it cannot be revitalized.
After a month of fighting in Iraq, the ISIS insurgency has made considerable progress, even if there is now something of a stalemate as Shi'a militias organise themselves and the weak Iraqi Army gets a measure of support from Russia, the United States and especially Iran.
After the death of Osama Bin Laden in May 2011, the global jihadist movement seemed to have become fragmented and considerably weakened. This happened for various reasons.