My feeling on the topic is that for the reason that we don't want nuclear exchanges every few pages and for realism only a few countries should have nuclear weapons. The three US's, the UK, France, China, me, South Asia and the Caliphate are quite enough.

The only reason that the US would need nuclear weapons there is if they were intermediate-range missiles (not ICBMs) and they needed to hit nearby countries. And considering you're in the middle of impoverished Africa with a distinct lack of advanced military might that doesn't seem likely. If I suspend my disbelief on that, however, they would be only capable of hitting other countries in Africa, but that might be enough for your needs.