One of the more shocking recent testimonies regarding Islamic State comes from Yazidi girls captured during the assault on Mount Sinjar in August 2014. The girls were immediately separated from their families and sold as sex slaves to Isis fighters. The justification for the sale and for their being bound, gagged and raped lies in the Qur’an, which, according to this interpretation, states that raping unbelievers is an act of devotion to God. One of the brave followers of the black flag said that rape was a form of prayer and brought him closer to Allah.

Jason Burke, veteran Observer and Guardian correspondent and author of the bestselling Al-Qaeda, identifies the population explosion in countries such as Egypt and Tunisia as a major factor in the rise of Islamic militancy. Millions in their 20s, unable to find work or a partner, are drawn by the promise of a purpose, a thrill and, yes, sex. Fight well, make money, get yourself a girl. Isis is not the first to offer this, but it has taken it to a new level. But for me, the most shocking aspect of the Yazidi girls’ testimony is that God-fearing men believe their religion condones such acts. And yet it is not just rape that brings Isis fighters blessings. “Terrorism,” the self-proclaimed caliph of Isis has said, “is to worship Allah as He ordered you.”

All this may feel far from your own sense of reality. There may be no one engaged in terrorism in the name of Allah in your street, no one drawing closer to their God by raping pre-teens in your back yard. But as Burke’s important and impressive book makes clear, what is happening to the benighted people of Iraq and Syria, and Libya, and Egypt, and of many other countries, touches us all and, increasingly, in ways we cannot ignore. If you have felt a frisson at the sight of heavily armed police and army at our railway stations and airports, then, according to Burke, you are already a victim of terror, though there is much more to scare you.

In a crowded field, The New Threat from Islamic Militancy is the most accessible and up-to-date analysis of the development of Islamic militancy. It gives a clear and convincing account of the evolution through the 20th century of the philosophy that seeks to justify this particular brand of terror. It looks at the consequences of the world-changing events of the late 1970s, from the Iranian revolution, to the immense wealth generated by oil price hikes, to the Soviet invasion of Afghanistan: Osama Bin Laden, after all, was a US-funded participant in the fight against the Russians. It considers the consequences of the misguided Iraq wars. It tracks the collapse of regimes in the Arab spring of 2011, the shift of regional power bases and the widening gulf between Sunni and Shia. But instead of throwing light on the deceptions or ineptitudes of our own leaders in all this – and how hollow does George W Bush’s triumphal 2003 “mission accomplished” speech sound now? – Burke keeps his sights fixed on the movements of Islamic militants. The view is consistently fascinating.

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Osama Bin Laden did not attack the World Trade Center because he wanted to kill people but because he was failing to attract attention for his pronouncements. 9/11 was tactical. It may also have outstripped even his ambitions because after it, the world’s media was only too happy to echo every word he spoke. Perhaps more significant, since then, we the world’s bystanders have known that anything could happen at any time, anywhere. One of the successes of Burke’s narrative is the way Bin Laden and al-Qaida come across as old-fashioned, at least in comparison with the current leader of Isis, al-Baghdadi, whose speech in the newly captured Iraqi city of Mosul last year moved the millennial clash of civilisations into another dimension. Bin Laden had looked with longing at what he saw as the golden age of the long-departed caliphate. Al-Baghdadi trumped him by declaring that Allah had chosen him to be the new caliph. Al-Baghdadi’s publicists uploaded footage of the speech on to the internet immediately after he had spoken.

The new threat of Burke’s title is not just the savagery of raping young girls, or beheading scores of orange-suited captives across the Middle East and North Africa. It is also in the random nature of attacks in our own countries – Lee Rigby, Charlie Hebdo and many others – and in our heightened awareness of the possibility of such acts. Bin Laden and al-Qaida had an issue with the foreign subjugation of Muslims and, specifically, with a US presence close to the holy sanctuaries in Mecca and Medina. Al-Baghdadi seems to have an issue with non-Muslims generally. It may be that he would like us all to convert or die. That he appears not to be aiming at us directly should make us worry more, especially when his fighters believe their God is pleased by the rape of prepubescent girls.

The New Threat from Islamic Militancy is published by Bodley Head (£16.99). Click here to buy it for £12.99