On the outskirts of Baga Sola, a small town in Chad not far from the border with Nigeria, is a refugee camp called Dar es Salaam. The name means “haven of peace”, but the surrounding area is an inferno of war, spilling across the borders of four countries: Chad, Nigeria, Niger and Cameroon. Some 2.4m people have been forced to flee the fighting.

The most obvious cause of their suffering is ideological. The jihadists of Boko Haram want to establish a caliphate, snuffing out such sins as Western-style education and imposing a harsh form of sharia (Islamic law) as the sole system of government. To this end, they torch villages, behead aid-workers and enslave or strap bombs to young girls.