What role did the Atlantic slave trade play within European competition during the colonial era?

During the colonial era, the Atlantic slave trade played a huge role by being competitive. During this period, colonies had started to develop and there were many prevalent African societies in European continent that had been there much before this era. They felt as a responsibility themselves to make a substantial contribution to the colonial era and hence they co-operated with the fellow Europeans to sell their own African slaves into slavery. Such slaves were their own who they kept for themselves before.