[Are you asking about the damage in life and infrastructure of Africa? Or the Global consequences of unleashing such an attack?]
'Both.'
[Do I assume that they all intend to hit a populated city center? Or a remote location?]
'Populated.'
[The immediate explosion from 5,800 simultaneous nuclear detonations would completely vaporize the city. Every building, structure, and piece of infrastructure within a 100-150 mile radius would be obliterated.]
[Within the Core Explosion or within 10 miles, In the aftermath of the initial blasts, firestorms would rage, burning anything that remains and creating a secondary, massive source of heat and destruction up to 100 miles away.]
[Temperatures would reach thousands of degrees Celsius in the immediate vicinity. This zone would have a 100% mortality rate. The Secondary zones or those between 10 and 50 miles are a bit better.]