The Sokoto Caliphate (1804–1903) was the vast Islamic state of the central Sudan, in what is now northern Nigeria and beyond. Founded by the Fulani scholar Usman dan Fodio through a jihad against Hausa kingdoms he judged corrupt and only nominally Muslim, it became one of the largest and most populous states in nineteenth-century Africa: a confederation of emirates bound by Islamic law and learning, sustained by farming and one of the largest systems of slavery in the modern world. The British conquered it in 1903 and then ruled through its emirs, so that its institutions and the Sultan of Sokoto's authority outlasted the empire itself.
It began with a teacher's complaint. Usman dan Fodio was a wandering Fulani scholar who preached in the towns of Hausaland, telling crowds that their kings taxed them unjustly, mixed Islam with older customs, and called themselves Muslims while behaving like tyrants. The kings tried to silence him. In 1804 he and his followers fled, declared a holy war, and within a few years had toppled most of the Hausa thrones. Out of a scholar's sermons grew the largest state in nineteenth-century Africa, a caliphate of thirty-odd emirates stretching across the savanna. It was built on faith and learning, and on the labor of more enslaved people than almost any other society of its age. A century later, British guns ended it. But the British kept its emirs, so the empire that a teacher founded still echoes in northern Nigeria today.