Excerpts from Books and Wikipedia
"Charles V (24 February 1500 – 21 September 1558) was ruler of both the Holy Roman Empire from 1519 and the Spanish Empire (as Charles I of Spain) from 1516, as well as of the lands of the former Duchy of Burgundy from 1506." [Wikipedia] "The official granting of the first Asiento in 1518 (the Spanish term means 'agreement' or royal 'assent' ) to license and approve the slave trade was one of the first major acts of the youthful Holy Roman Emperor Charles V upon coming to the Spanish throne. . . . The first recorded cargo of black slaves from Africa landed in the West Indies in the same year that the first Asiento was granted. Charles V later withdrew his approval of the slave trade, passing laws banning it in 1542. . . . However, the slave trade continued unabated. Portuguese merchants bought slaves from dealers in the Upper Guinea and Sierra Leone regions of West Africa and shipped them to the Americas. . . . By the early seventeenth century, some 85 percent of slaves arriving in Spanish ports in the Americas were from Angola, shipped by the Portuguese." [Furtado: 1001 Days]