One difference between ISIL and other Islamist and jihadist movements, including al-Qaeda, is the group's emphasis on eschatology and apocalypticism – that is, a belief in a final Day of Judgment by God, and specifically, a belief that the arrival of one known as Imam Mahdi is near.
It's a big selling point with foreign fighters, who want to travel to the lands where the final battles of the apocalypse will take place.
The civil wars raging in those countries today [Iraq and Syria] lend credibility to the prophecies. [...] For Bin Laden's generation, the apocalypse wasn't a great recruiting pitch.
Governments in the Middle East two decades ago were more stable, and sectarianism was more subdued.
For their guiding principles, the leaders of the Islamic State ...
are open and clear about their almost exclusive commitment to the Wahhabi movement of Sunni Islam.
Specifically, ISIL has sought to establish itself as a caliphate, an Islamic state led by a group of religious authorities under a supreme leader – the caliph – who is believed to be the successor to Prophet Muhammad.