In the Caribbean, Dutch Guiana, and Brazil, the slave death rate was so high and the birth rate so low that they could not sustain their population without importations from Africa. Rates of natural decrease ran as high as 5 percent a year. While the death rate of US slaves was about the same as that of Jamaican slaves, the fertility rate was more than 80 percent higher in the United States.
US slaves were more generations removed from Africa than those in the Caribbean. In the nineteenth century, the majority of slaves in the British Caribbean and Brazil were born in Africa. In contrast, by 1850, most US slaves were third-, fourth-, or fifth generation Americans.
Slavery in the US was distinctive in the near balance of the sexes and the ability of the slave population to increase its numbers by natural reproduction. Unlike any other slave society, the US had a high and sustained natural increase in the slave population for a more than a century and a half.