In the summer of 2014, hundreds of Islamic State (IS) militants fanned out through the Sinjar region of northern Syria, the ancestral home of the Yazidi people, murdering many of the able-bodied men and dragging off many of the women and girls to be ‘slaves’. By the time I arrived in Sinjar five months later, almost all international reporting of events there, to the annoyance of many locals, had been reduced to nakedly voyeuristic stories about rape. A good many of the Yazidi women I met had indeed been raped, but many others had not; beyond the tabloid headlines the underlying story was one of simple political economy. By distributing Yazidi women to its supporters as booty, who could then be sold on the open market and back to their families for around $20,000 each, IS was plugging a hole in its finances, and turning local Sunni Muslims and Yazidis against each other.

Loretta Napoleoni’s new book is an attempt to work out what this new wave of international kidnapping, from Syria to Nigeria, can tell us about how modern terrorism and criminal networks operate. Napoleoni, an astute Italian investigative journalist who begins by following the money, notes that IS’s enthusiasm