The transatlantic trade involves the movement of the slaves for the shores of the Atlantic coast to the Africa to that of the America for working as bonded laborers. And mostly these formed the central and the western African. The demands were created by the Europeans as they discovered the new lands and they began to migrate and settle which needed the human labor.
Thus Lead to a triangular slave trade as the export of the goods from Europe to America took place through the help of the African slaves, and was fir the Atlantic ocean and the Caribbean sea.
As the demand for slaves grew, the Portuguese began to enter the interior of Africa to forcibly take captives; as other Europeans became involved in the slave trade, generally they remained on the coast and purchased captives from Africans who had transported them from the interior.