Portuguese traders had already set up shop there, traded, and even educated some Kongo Nobility. Then the Kingdom of Kongo attempted to fight the portuguese with dutch aid. Didn't work.
I'm sorry, I don't know enough info about sub-saharan africa. But the potential for a strong state is there and it shouldn't go to waste in AH.com.
For starters, one should try to avoid the Kongo Civil War (1665-1709) which I think was a war fought between branch families of the royal family.