It should be pointed out that this is a unilateral declaration by a group seeking greater cachet among fervent [Sunni] believers, not a declaration by "the Muslim world" as a whole. If you do not control the Holy Places, you can't make much of a claim to Caliphate in the broadest sense; if you are a tiny fraction of the world's Muslims, even less so. There was not, and is not, a single predominant Islamic power that could reliably make the claim to true succession from the Prophet and have it taken seriously. The Ottomans, on the other hand, controlled an enormous percentage of the Islamic world in the 16th and 17th centuries, which is why they could take it on--but whether the Ottoman claim ever carried the weight it had for earlier Caliphates is doubtful.

[edit: As a follow-on question for the Islamic 20th-C. specialists, is this the first time a group or entity has sought to proclaim that connection? I'm not aware of the Saudis ever trying, and I can't imagine they would be happy about anyone else doing it either.]

Additional question: has anybody ever seriously floated the idea of having a caliph, but having him be more like the equivalent of a pope, with no real power, but acting as a spiritual leader?

Removed. This is a bit of a borderline case, but this question was attracting FAR too many responses regarding current events, which is against our subreddit rules.

If you would like to repost without mentioning the recent selection of Caliphate, you may. Something along the lines of "Why wasn't there any move to continue the Caliphate post-Ottoman empire?" perhaps.

For a significant amount of time, the Caliphate was held by the Ottoman Empire, who were seen as the Turkish overlords for a variety of Arab nations/tribes/whatever, so for a political entity to declare itself a caliphate is to declare its right to subjugate other current Islamic states which were in the past under the authority of that medieval entity.

There are several recent news articles I've read, about why Turkey needs to proceed carefully in Syrian intervention, precisely because of the loaded history of their state as a previously expansionist/imperial "caliphate," so it's not hard to imagine that it would've been with caution that other entities sought to avoid that term outright.

I wonder, if in fact the specific desire of militants to recreate an Islamic caliphate, is itself their answer to western globalization; a globalization of the wider Islamic community.

the rules of this sub state:

No current events To discourage off-topic discussions of current events, questions, answers and all other comments must be confined to events that happened 20 years ago or more (1994 or older).