There are many ways in which this question can be answered. As yu can imagine, there is a long history of European involvement in Western Africa. In light of this, let me give a few points.
First, the most obvious point to make is that Europeans have hurt Africa in that Europeans have exploited Africa for its resources. And most seriously, Europeans were involved in the Atlantic slave trade. Most of the slaves came from central and western Africa. Historian of this slave trade called is a Maafa, which means holocaust or "great disaster." In light of this, we can say that people power was taken away to hurt the economy.
Second, the Europeans established unfair trade agreements with African nations. In a word, Europeans just took advantage of the natural resources and commodities for their own gain. This eventually lead to the underdevelopment of African economies and the wealth of European nations. Ralph Austen, a historian of this time documents these points.