Islam has a deep history in north Nigeria, one punctuated by regular movements calling for purification and renewal. Usman dan Fodio’s 19th-century jihad established a conservative caliphate across the region. Although the caliphate’s capital was in Sokoto (now in northwestern Nigeria), the city of Kano became a center of commerce and Islamic learning that attracted migrants from across West Africa. To this day, northerners identify with the pre-colonial past, and traditional leaders such as the Emir of Kano adhere to Usman dan Fodio’s Qadriyya branch of Sufi Islam.
In the early 20th century, after the British conquest of north Nigeria in 1903, a purification movement challenged the dominant sect. The movement's adherents condemned traditional leaders for deviating from proper Islamic practice and – more damning – for compromising with imperial rulers.
The colonial experience established a persistent mistrust of Western motives that continues to this day, and a fear that Westerners seek to erode Islamic culture through Christian conversion. The vaccine crisis of 2003-05, when northerners rejected the polio inoculation as a plot to sterilize Muslims, was a recent expression of this fear.