From: https://www.thoughtco.com/african-slave-traders-44538
During the era of the trans-Atlantic slave trade, Europeans did not have the power to invade African states or kidnap enslaved Africans. Because of this, between 15 and 20 million enslaved people were transported across the Atlantic Ocean from Africa and purchased from traders of enslaved people throughout Europe and European colonies.1
One thing that many Westerners wonder about African enslavers is why they were willing to sell their own people. Why would they sell Africans to Europeans? The simple answer to this question is that they did not see enslaved people as “their own people.” Blackness (as an identity or marker of difference) was at that time a preoccupation of Europeans, not Africans. There was also in this era no collective sense of being “African.” In other words, African traders of enslaved people felt no obligation to protect enslaved Africans because they did not regard them as their equals.