Right now, in East Africa, we have al-Shabaab which has already overrun the country and is expanding into Kenya, with the mall killings in Kenya last year that were so appalling. In northern Mali, we have MUJAO which successfully captured the north for a long time before they were rolled back by French forces, supported by Nigerian forces, and so forth.
The sad thing is that, although the exact same thing is happening in Nigeria, I don't see the world coming together to help Nigeria roll back Boko Haram the way Nigeria helped the French roll back MUJAO.
In that region of the African continent, those are a few countries that are clearly under threat.