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''Listen to your caliph and obey him. Support your state, which grows every day,'' said Abu Mohamed al-Adnani, announcing the rebirth of the caliphate in the broad territory between Aleppo in northern Syria and Diyala province in eastern Iraq.
It hasn't grown much more in the past couple of weeks, but it certainly intends to go on expanding.
The radical Sunni Muslim organisation that conquered almost half of Iraq in a whirlwind week at the beginning of June now wishes to be known simply as the ''Islamic State'' - for there can only be one such state, and it should include everywhere Muslims have ever ruled.
Isil propagandists have produced a map showing the ultimate borders their Islamic State lays claim to. Spain and Portugal will be part of it, because they were ruled by Muslim conquerors during much of the Middle Ages. Iran, too (although something will have to be done about all those Shia Muslims).
All of India except the southern tip should be under the rule of the Caliph, because Muslim invaders also ruled there as minorities for many centuries, and Serbia, Croatia and Hungary will be part of the Islamic State, for the Ottomans conquered all the Balkans up to there. Not to mention half of Africa, and Indonesia, and southwestern Siberia (ruled by the Sibir Khanate for a century or so).
There's no point in protesting that Muslims were never more than a small minority in many of these places, for the lads of Isil believe that only Muslims - indeed, only Sunni Muslims - have rights.
''The legality of all emirates, groups, states and organisations becomes null by the expansion of the Caliphate's authority and the arrival of its troops to their areas,'' al-Adnani explained.
So much for the fantasy. What's the reality? A group of jihadis have seized a big chunk of eastern Syria and western Iraq, erased that border, and declared an Islamic State. As few as 10,000 strong only a month ago, they have been rapidly growing in numbers as Isil's success attracts new recruits - but they are obviously never going to reconquer India, Spain or Siberia or make a dent in Iran or Turkey.
To the west and east Isil is already at war with regimes that are either very tough (Bashar al-Assad's war-hardened dictatorship in western and central Syria) or very Shia (the southeastern slice of Iraq, densely populated and with a large Shia majority). The Islamic State's central position between its two enemies gives it a strategic advantage, but not a decisive one.
To the south are desert frontiers with more promising territory. Jordan's population is about two-thirds Palestinian, and even among the Bedouin tribes that are the mainstay of King Abdullah's rule there was some enthusiasm for Isil's victory in Iraq. If Jordan fell, the Islamic State would reach right up to Israel's borders, with incalculable consequences.
Saudi Arabia would be a much tougher nut to crack, but the salafi religious ideology that animates Isil is very close to the fundamentalist Wahhabi version of Islam that is the Saudi state religion.
But even if Isil gets very lucky, it is unlikely to get farther than that. Egypt blocks its expansion to the west, although the Ansar Bayt al-Maqdis extremists who are active in the Sinai peninsula undoubtedly have some ties with it. Even its direct rivals in the Refound-The-Caliphate business - the original al Qaeda, al-Shabab in northeast Africa, Boko Haram in northern Nigeria, and their lesser brethren - are unlikely to accept the Isil leader as caliph.
Abu Bakr al-Baghdadi, who now styles himself Caliph Ibrahim, has clearly been preparing himself for this moment for most of his adult life: he even chose the name of the first caliph, Abu Bakr, as his nom de guerre. His spokesman does not hide his soaring ambition: ''We hereby clarify to the Muslims that with this declaration of Khilafah (caliphate), it is incumbent upon all Muslims to pledge allegiance to the Khalifah Ibrahim and support him.''
They are not going to do that, and the sheer radicalism and intolerance of Isil's members make it unlikely their project will survive unaltered for more than a year or so even in the territory that now makes up the ''Islamic State''. Nevertheless, it is extraordinary the 7th-century caliphate has reappeared even fleetingly in the modern world. Bush and Blair have a lot to answer for.
- Gwynne Dyer is an independent London journalist.