My colleague, Shafik Mandhai, is a graduate in Islamic Studies. He wrote some background and analysis on what kind of caliphate the Islamic State group thinks it is creating, and whether it will be accepted, which I am reposting below:
The caliphate is an emotive issue for many Sunni Muslims. Abolished with the Ottoman Empire in 1924, its return has been a key aim for armed groups like al-Qaeda and ISIL.
But it’s not the Ottomans the Islamic State wants back.
Fighters under the command of Abu Bakr al-Baghdadi, or "Caliph Ibrahim", want to re-establish the Rashidun caliphate, which succeeded the Prophet Muhammad in the 7th century.
The caliph served a dual role as religious and political head of the Islamic nation, or "Ummah", a position that does not currently exist except for those who have heeded Baghdadi’s call for "Bayah" or allegiance from all Muslims.
The Rashidun caliphate, unlike all those that followed it, had near-universal allegiance from the Muslim community, something the Islamic State cannot claim to enjoy. However, its supporters can still find parallels.
Supporters of Baghdadi will point to his organisation’s fierce literal interpretation of Islam, which they say accurately reflects the rule of the early caliphs.
Baghdadi, they say, also meets the theological requirements for leading the Ummah, including descent from the Prophet's Quraish tribe.
It’s likely the Islamic State and its supporters will also find precedent in the historical conquests of the Rashidun caliphate - rapid military conquests against a better equipped enemy.
The rapid spread of Islam in the 7th century is something the Islamic State clearly intends to emulate, and their fighters will no doubt have been buoyed by their recent gains in Iraq.
Where the Islamic State’s bid to establish a caliphate begins to falter is acceptance from other Muslims.
It has even earned the rebuke of al-Qaeda's core leadership, including Ayman al-Zawahiri, over its brutality against prisoners and its repressive implementation and interpretation of Islamic teachings.
The Nusra Front, al-Qaeda’s primary affiliate in Syria, has been battling the Islamic State since an unsuccessful attempt by Baghdadi to forcibly merge the groups in 2012.
Whether Baghdadi’s caliphate will gain legitimacy among others who wish to establish it will depend on whether al-Qaeda’s affiliates in North Africa, Somalia and Yemen break ranks with its central command.
There also remains the important matter of withstanding offensives by the Syrian and Iraqi regimes, rival Syrian rebels, and possible Western intervention.