If we compare Africa to South America purely in economic terms, South Africa is Argentina and Nigeria is Brazil.

South Africa, a country primarily composed of white people, holds the top GDP in Africa.
Argentina was a country that opened a subway system in its capital, Buenos Aires, back in the 1930s. It was once the wealthiest country in South America.
Nigeria has a massive population advantage, much like Brazil.
There are predictions that its population will surpass that of the United States by around 2050.
It already became the top GDP country in Africa about 10 years ago, driven by its population power.