BBC reporter Andrew Hosken illuminates the backstory of the richest terrorist group in the world, the Islamic State (also known as ISIS, the Islamic State of Iraq and al-Sham), in Empire of Fear: Inside the Islamic State (Oneworld Publications, Sept. 1). The book explains how ISIS was formed, what their goals are, where they are now, and what should be done to combat their efforts.

Yours is one of the few books on ISIS by journalist with on-the-ground experience in Iraq – tell me about your work there, and the reasons why you wrote Empire of Fear.

I was sent there three times during 2013 and 2014 for long stints, and I was there in June and July 2013 when ISIS threatened Baghdad. I was there on the day the caliphate was declared and when ISIS leader Abu Bakr al-Baghdadi declared himself Caliph. I was reporting on this growing menace, on the upsurge of violence that preceded its military offensive in January 2014.

I want this to be a book for people who don’t know anything about ISIS, who read about it in the paper and see these horrible stories on TV, and ask like in Butch Cassidy and the Sun Dance Kid, “Who are those guys?” They’re not a part of Al Quada, they’re a separate phenomenon; they have a separate agenda and are much more sinister.

In addition to writing about your own experiences, you personally interviewed U.S., U.K., and Iraqi officials as well as clergy and religious leaders of all faiths. Can you describe some of the insight people of faith had on ISIS?

One of the terrible tragedies in Iraq is the fate of Christians, who were a central part of Iraq. I think there are more Iraqi Christians now in the state of Michigan than there are in Iraq. There were 1.2 million Christians living in Iraq in 2003; today there are 400,000, and most want to leave. I interviewed Reverend Canon Andrew White (vicar of the sole Anglican church in Iraq); he lost a quarter of his flock who were persecuted or forced to pay a tax or be killed. I asked myself, why has the Christian population gone down? It’s ISIS. The terrible violence, you wouldn’t believe it—what they did to people’s children, the churches they blew up and the number of people they have killed. I cite a report in the book about ISIS cooking a two-year-old Syrian girl and serving it to her family.

Can you describe what life is like in Iraq?

When you’re there, you think at any moment a car bomb could go off. I don’t know what it feels like to wear an orange jumpsuit and about to be murdered by a coward with a knife, but I do know what it feels like to live among ISIS. I describe it as living on one big death row, on death row all the time, and ISIS makes it feel that way.

The Islamic State is recruiting thousands of people to their ranks, including Americans, and especially young people. How does such a horrifying group attract anyone?

It’s a complicated answer. I’ve been speaking to extremists in the UK, including one whose passport was taken by the British government because he wants to go to Syria and join. I asked him why and he said, “I don’t believe anything in the Western media.” I asked about the children being crucified, the people being burned to death and beheaded, he said he didn’t believe the videos.

More reasonable people, like in Northern England in Bradford, say segregation there is now so strict that entire schools are just Muslims and others are Christian white kids—people aren’t mixing as they used to. There is Islamic-phobia, people fear their culture, despise it. Muslims see ISIS is horrible and evil, but they are self-confident and say, “This is our land, come be part of this new Islamic paradise.” Of course, it’s not a paradise, but propaganda promises food and land, and no journalists are allowed in to report the truth. ISIS is sending the message, “Leave people who hate you and hate Islam and join us.”

ISIS is especially dangerous for women; yet hundreds of young girls join weekly.

There is actually a British girl who says, “Come marry these handsome soldiers,” but this is an organization that prints books from their own publishing house about when and how they can rape 13-year-olds, and how to treat slaves. Women are habitually raped and used as slaves; this is the reality. I’ve talked to people who have seen one 13-year-old stoned to death, and her father was forced to participate—appalling, especially for women who are beaten and flogged for showing their hands or face. Why girls are going is incredible.

What is one thing you would like readers to understand about ISIS?

ISIS is a relentless menace that will not stop until basically the world doesn’t include most of us. ISIS doesn’t want to just exclude people; they must be killed. You cannot accommodate someone who wants to kill you. Everyone, all Christians, all Shiite, all the people who do not subscribe to their narrow, weird, frightening interpretation of Islam must be killed, no ifs or buts. That is what this is all about. This is also by far the richest terrorist organization. They have vast oil supplies, they sell everything from people to antiquities, oil, and this has potential to get worse.