I would hesitate to call slaves that were involuntarily relocated from their old masters in Africa to their new masters in the new world as “migrants”. Perhaps others can tell me if it is true, but weren't most of those “migrants” used to replace slave labor that died in the plantations of Brazil and the Caribbean?
“the vast majority of transatlantic migrants (more than 80 percent up to 1820) came from Africa labor to replace the disease-defeated Amerindians”
It’s moreso the fact that a lot of the native americans were less like the settled Aztecs and more like hunter-gatherers. Governments conquer and regularize kleptocracy over agrarian and later city-dwelling peoples, not mobile peoples. You can’t make slaves out of people that can run for the hills.