The Virginians were desperate for the labor in their lands, in order to grow enough food to stay alive.
They first thought about the Indians for slaving purposes. But, they could not force them because they were outnumbered. They could not capture them and keep them enslaved; the Indians were tough, resourceful and defiant.
And White servants had not yet been brought over in sufficient quantity. Besides, they did not come out of slavery
Black slaves were the answer. Their helplessness made enslavement easier.
On the coast, the black men and women were kept in cages until they were picked and sold. Then ship's surgeons examined every part of every one of them, to the smallest member, men and women being stark naked. Finally, they were marked and they awaited the shipment.
Then they were packed aboard the slave ships, in spaces not much bigger than coffins. And here they are usually chained to the decks by the neck and legs. A slave-deck was "so covered with blood and mucus that it resembled a slaughterhouse."