Nigeria has had multiple constitutions since the colonial era, which were modeled on the British constitution and, more recently, on the American constitution. The current Nigerian constitution (1999), explicitly states that there will be no state religion, supports the free expression of religion, and prohibits discrimination on the basis of religious belief. In reality, political life reflects a more complicated engagement with religious identity that varies by religion, ethnicity, and region.
For example, there are complaints on the part of Muslims and Christians alike that political leaders show favoritism toward citizens and groups that share their religion, and stoke sectarian violence when it suits their purposes. On one hand, many Nigerians sense that their religious group is underrepresented or unfairly excluded from the political realm on the local, state, or national level, though the election of Buhari may have altered this feeling. On the other hand, Christians in the South express fears that the army and defense positions are dominated by northern Muslims.
There are also concerns over the relationship between politicians and the religious experts they often patronize in order to gain access to political power. It is widely known that some politicians across political parties enlist the services of religious experts (sometimes from two or three traditions at the same time) to ensure victory in elections, or to consolidate power. Apart from some of the ethical issues raised by some of these activities and the way they are reported and/or perceived, there is concern over the potential subservience of political leaders to these religious experts.
Finally, the constitution also permits individual states and regions to utilize common law (including religious law) in local courts, and thus legislative processes differ across Nigeria’s thirty-six states and Federal Capital Territory. State governors and state legislatures enjoy significant autonomy in decision-making, and the 1999 constitution allows permits to establish courts based on common or customary law systems.
Consequently, Nigeria’s constituent states have been allowed to institute Islamic law (shari’a) as the basis of local civil and court procedures. In 1999–2000, with Muslim politicians leading the effort and garnering support from a populace disappointed with corruption in the national legal system, all twelve northern states elected to do so. Some Islamist groups, including Boko Haram, view Islamic law as the sole legitimate source of political authority. However, the adoption and practice of Islamic law has received a mixed response among Muslims, with some preferring the status quo before its adoption.
 John Campbell, “Religion and Security in Nigeria,” in The Routledge Handbook of Religion and Security, eds. Chris Seiple et al. (New York: Routledge, 2013), pp. 215–225.