I understand that Native Americans were enslaved in certain cases, most notably by Christopher Columbus in Puerto Rico. However why is it that the primary enslaved population in the Americas were African? From both an economic and convenience perspective it seems odd that people from Europe would travel to Africa to then travel to America and produce crops to then... send back to Europe? Or at least send the profits back. Why not just enslave other Europeans? Or simply bring African slaves to Europe, rather than risk the financial and human loss of transporting them to a tertiary location even farther away? Even simpler, why not just conquer Africa and grow the crops there? Certainly that was already happening, so why take all these extra steps? There are some obvious factors I'm missing here, any explanation that can shed some more light on the economics of colonialism would be appreciated.
I had written a long reply to a deleted comment and I would still like to post part of my response related to Indigenous slavery. Indigenous people were enslaved in large numbers and their depopulation did force Europeans to look elsewhere for labor. However, the power of Indigenous nations played a large and oft-forgotten role as well. Indigenous groups maintained tremendous power on the continent and Europeans were incapable of forcing their will on them for most of the early colonial period. As late as the Seven Years' War, primarily Indigenous forces from the Ohio River Valley actually succeeded in rolling back the British "frontier" in Pennsylvania to within a hundred miles of Philadelphia. Ironically given the initial incorrect answer's premise, during the same conflict thousands of Europeans were captured in the Middle Colonies and taken west as captives and sometimes performed forced, enslaved labor.
In the South, the British initially relied on Indigenous allies to help enslave Native peoples, but this came to a head in the Yamasee War in which the colony of South Carolina was nearly lost to an Indigenous coalition. In the aftermath of the conflict, the "Indian Slave Trade" was seriously curtailed to avoid once again raising the fury of the colony's Indigenous neighbors.
In New France, recent work (Brett Rushforth's Bond's of Alliance) has argued that some Indigenous groups actually entangled the French in a system of slavery that they did not understand in order to sabotage French efforts at expanding an imperial alliance to the west. By selling their enemies to the French (who subsequently sent the enslaved individuals into the wider Atlantic), these groups ensured that their enemies would refuse to enter into peaceful relations with New France.
Depopulation still played an important role, as disease and violence took their toll on Indigenous populations or those populations migrated to avoid interacting with Europeans. However, one of the most significant and overlooked reasons for why Europeans looked elsewhere for enslaved labor was because they were too weak to force large populations into slavery in North America. When they used Indigenous allies to overcome this weakness and gather an enslaved labor force, they were often entangled in disastrous conflicts that they barely survived.
A few works that explain this in greater detail are:
Bond's of Alliance: Indigenous and Atlantic Slaveries in New France by Brett Rushforth
The Indian Slave Trade: The Rise of The English Empire in the American South, 1670-1717 by Allan Gallay
Our Beloved Kin: A New History of King Phillip's War by Lisa Brooks
Since there have been a couple of deleted answers here already, and it seems there will continue to be more posted if a quality answer doesn't get posted and stay up, I will point you to this great answer by u/anthropology_nerd. In short: for quite a while, American Indians were the primary population to be enslaved, and it was only because Europeans so thoroughly worked them to death so often that the Europeans began to import enslaved people from Africa.
There's always more that can be said, but you might enjoy these older threads from /u/anthropology_nerd. To put it somewhat simply, they were enslaved at times and places and in significant numbers.