Why are there Black people in Brazil, Jamaica, etc?

K I am really wondering about this. Black people are from Africa right? So why are there black people in Brazil, Jamaica, and Haiti? I can only figure that it was when the tectonic plates shifted and the continents split up. I know that's what happened to the dinosaurs, so did some black people just get trapped on the South American side when the continents split up? Sounds right, right?