Nigeria is the most important country in sub-Saharan Africa if only because one fourth of the total population of the region lives there. Boko Haram, the fanatical group whose name means “Western knowledge is unclean,” wants to plunge Nigeria into a vast sectarian war.This weekend bombers believed to be linked to the group took another step toward their goal. The news accounts conflict, but something around eight people were killed and perhaps 100 were wounded in an attack on a Catholic church during Mass. In the aftermath of the attack in the northern city of Kaduna, gangs of young men from Christian communities were witnessed looking for revenge. Some carried knives and were covered in blood.Migration and conversion have created Christian communities in some northern Nigerian cities that were once almost exclusively Islamic. What many see as the rising political, economic, and demographic power of Christians in the oil rich African nation has alarmed some northern leaders, and there are signs that Boko Haram at various times has had help from elements in the northern power establishment, which ran the country for many years.To date wiser heads and calmer counsels have kept a lid on the potentially explosive violence between Nigeria’s two religions, but the future offers no guarantees. Both the Christians and the Muslims in this country have been shifting toward more aggressive forms of their faith, and Christians in particular are thinking about organizing in their own self-defense.As the turmoil shaking the Middle East penetrates deeper into Africa, weak states and poorly developed countries will be coping with some of the most difficult and explosive challenges of our time.