Your answer is A. Created an expansion of the African slave trade
B is incorrect, because African people didn't get to rule themselves. If anything, Europeans got more and more entangled in their affairs.
C is incorrect, the slave trade devastated the African population, and the demographic was really lopsided and disproportional. There were more women than men.
D is incorrect, because tribal conflicts continued. Tribal chiefs struck deals with the Europeans to sell their people into the slave trade.