Okay, Sub-Saharan Africa was historically bypassed by trade going back to antiquity. Then, when colonial powers set up in the scramble for Africa, they would set up segregated societies bent on keeping white colonials in power. Once they left, they did so with no concern for the transfer of power, often leaving warlords to consolidate hold over territory. These warlords would consolidate power to their own family and friends with no regard for governance. Often when people organized for rights and justice they were brutally repressed, resulting in many genocides based on existing ethnic tensions.
Furthermore, the borders drawn by the colonial powers didn’t go away once the powers left. These borders, often separating ethnic groups are a continuous point of conflict between the powers that be.
Europe, on the other hand, has been stable for 75 years, and has since focused heavily on economic cooperation between states rather than using war as a balance of power between states. Peace has led to continued economic development, and cooperation has facilitated that in the modern era.
Historically, you cannot deny the racism evident in the colonial european powers which siphoned resources from the native populations by military force.