Relations between the two countries, long bound by common interests in oil and security, have strained over what some analysts see as a more assertive Saudi foreign policy.

Boko Haram, known for mass kidnappings, bombings, and other acts of terrorism, remains an enduring threat to northern Nigeria and the Lake Chad Basin.

Nearly all nuclear weapon states, as a matter of policy, remain ready to use their weapons without having first suffered a nuclear attack.

As the campaigns to wrest the Islamic State from the territory it held in Iraq and Syria near completion, new conflicts may arise if old political arrangements prevail.