Nigerias stability has been repeatedly threatened by fighting between fundamentalist Muslims and Christians over the spread of Islamic law (sharia) across the heavily Muslim north. One-third of Nigerias 36 states is ruled by sharia law. More than 10,000 people have died in religious clashes since military rule ended in 1999.

In 2003, after religious and political leaders in the Kano region banned polio immunization—contending that it sterilized girls and spread HIV—an outbreak of polio spread through Nigeria, entering neighboring countries the following year. The Kano region lifted its ten-month ban against vaccination in July 2004. On Aug. 24, there were 602 polio cases worldwide, 79% of which were in Nigeria.

Since 2004, insurgency has wreaked havoc in the Niger delta, Nigerias oil-producing region. The desperately impoverished local residents of the delta have seen little benefit from Nigerias vast oil riches, and rebel groups are fighting for a more equal distribution of the wealth as well as greater regional autonomy. Violence by rebel groups has disrupted oil production and reduced output by about 20%. Nigeria is one of the worlds largest oil producers and supplies the U.S. with one-fifth of its oil.

In Aug. 2006 Nigeria handed over the oil-rich Bakassi peninsula to Cameroon, in compliance with a 2002 World Court ruling.