Slavery is not an institution that developed itself. Many people used the Bible as their justification of slavery. In the book of Genesis, chapter 9, Noah's youngest son Ham saw the nakedness of his father and had him covered, by his brothers. Noah then cursed Ham to be a servant to his brothers forever, Genesis 9:25-26 "Cursed be Canaan! The lowest of slaves will he be to his brothers". This is known to be the first act of slavery; which people argue is sanctioned by God. Many interpret Ham's curse as placed upon people of darker skin color, Africans more specifically. The argument is that since Ham's descendants were to be slaves forever and Africans were already slaves and inferior then they should remain in slavery.
These populations continued to grow at a rapid rate throughout the 18th century made up as much as 80% of the population in Virginia in the 17th century.