All slave economies in the New World worked roughly as follows.
1. There was a white planter class.
2. There was a black enslaved class.
3. There was another class of free laborers in the middle.
In more tropical climates, there were not many free whites who settled, as the environment was very unhealthy for those of European descent. As a result, the middle rungs of society ended up filled free persons of mixed race. While these people would not be visibly white, they would be whiter than the slaves, and identify culturally with the mother country, due to the comparable privilege their whiter blood gave them.
But in the U.S., a free mixed-race middle class wasn't needed. The climate wasn't quite as bad as in the tropics, and a large free white population was established. The middle class being white, there was no reason to allow for a creole identity to be formed, and thus mixed-race people firmly kept their black identity, and indeed were nearly as frequently slaves once racial lines hardened.
1. There was a white planter class.
2. There was a black enslaved class.
3. There was another class of free laborers in the middle.
In more tropical climates, there were not many free whites who settled, as the environment was very unhealthy for those of European descent. As a result, the middle rungs of society ended up filled free persons of mixed race. While these people would not be visibly white, they would be whiter than the slaves, and identify culturally with the mother country, due to the comparable privilege their whiter blood gave them.
But in the U.S., a free mixed-race middle class wasn't needed. The climate wasn't quite as bad as in the tropics, and a large free white population was established. The middle class being white, there was no reason to allow for a creole identity to be formed, and thus mixed-race people firmly kept their black identity, and indeed were nearly as frequently slaves once racial lines hardened.