The majority of people who emigrated to the Americas until 1820 were black slaves, and it wasn't because that's what everyone wanted in terms of a racial makeup, but rather because of the enormous and expandable flow of slave labor from Africa. Frederick Douglass, who was born into slavery, had to tell people that not only was he a slave for life, but his kids were slaves too, giving a vested interest in the slave trade, which changed over time to handle the labor shortage by different groups.