Boko Haram: Inside Nigeria’s Unholy War. By Mike Smith. I.B. Tauris; 233 pages; $29 and £18.99.

“YES, Western education is forbidden,” said the shirtless man with the bandaged arm. “Any type of knowledge that contradicts Islam, Allah does not allow you to acquire it.” It was July 2009, and the speaker was Mohammed Yusuf, the leader of a group of then little-known jihadists. The setting was a hasty interrogation that followed Yusuf’s capture after a brief uprising in north-eastern Nigeria sparked by a clash with policemen. A few hours later he was executed by security forces.

Rather than focusing on the usual subjects of such conversations—locations of weapons and quantities of soldiers, say—the interrogation took the form of a theological debate between two Muslims. Details of the encounter, which was recorded on video, shed much light on the contradictory and messianic world view of Yusuf, the founder of a group that has since become familiar to the wider world as Boko Haram, a name that loosely translates as “Western education is forbidden”. That the group takes exception to such teaching is all too plain. Last year it kidnapped more than 200 girls from a school in Chibok in north-eastern Nigeria that used Western teaching principles.

Boko Haram does profess a commitment to learning, but of a specific sort. Members prefer it to be known as “Jama’atu Ahlis Sunna Lidda’awati wal-Jihad”, which in Arabic means “People Committed to the Propagation of the Prophet’s Teachings and Jihad”. In its early days the group emphasised teaching rather than killing. Yet it took a radical, violent turn soon after Yusuf’s brutal death.

In the five years since, Boko Haram has spread havoc across parts of Nigeria, Niger, Cameroon and Chad. More than 10,000 people have been killed in related violence and as many as 1.5m driven from their homes. By the end of 2014 the group had conquered large tracts of three of Nigeria’s north-eastern states and had declared its intention to form a caliphate. More recently, it has proclaimed its allegiance to Islamic State (IS), a jihadist group that holds sway over parts of Syria and Iraq.

We don’t need no education

Much has been written about extremist groups such as IS and al-Qaeda, which directly threaten Westerners at home or abroad. But little is understood about Boko Haram, its leaders and its beliefs. This is partly because it has made little effort to explain itself to the wider world, unlike jihadists such as IS who reach out to potential recruits using social media, and partly because journalists are unable to enter territory it controls safely. Moreover, its limited regional focus means that most Western intelligence agencies have viewed it as posing little international threat.

This book by Mike Smith, a journalist, sheds light both on its crackpot ideas—Yusuf insisted that the world was flat and that rain was made by God—and on the deep contradictions faced by people who propose to return to a sixth-century lifestyle. When asked why he had computer equipment and hospital facilities at his home, Yusuf replied, “These are technological products. Western education is different. Western education is westernisation.”