Yet although IS is certainly an Islamic movement, it is neither typical nor mired in the distant past, because its roots are in Wahhabism, a form of Islam practised in Saudi Arabia that developed only in the 18th century. In July 2013, the European Parliament identified Wahhabism as the main source of global terrorism, and yet the Grand Mufti of Saudi Arabia, condemning IS in the strongest terms, has insisted that “the ideas of extremism, radicalism and terrorism do not belong to Islam in any way”. Other members of the Saudi ruling class, however, look more kindly on the movement, applauding its staunch opposition to Shiaism and for its Salafi piety, its adherence to the original practices of Islam. This inconsistency is a salutary reminder of the impossibility of making accurate generalisations about any religious tradition. In its short history, Wahhabism has developed at least two distinct forms, each of which has a wholly different take on violence.

A whole generation of Muslims, therefore, has grown up with a maverick form of Islam that has given them a negative view of other faiths and an intolerantly sectarian understanding of their own. While not extremist per se, this is an outlook in which radicalism can develop. In the past, the learned exegesis of the ulema, which Wahhabis rejected, had held extremist interpretations of scripture in check; but now unqualified freelancers such as Osama Bin Laden were free to develop highly unorthodox readings of the Quran. To prevent the spread of radicalism, the Saudis tried to deflect their young from the internal problems of the kingdom during the 1980s by encouraging a pan-Islamist sentiment of which the Wahhabi ulema did not approve.

This is fundamentally important.