The short answer is indigenous people throughout the Americas were enslaved, from the beginning of contact into the 20th century, and from the Southern Cone to the High Arctic. You cannot understand the impact of colonialism in the Americas without understanding to role of the indigeous slave trade.

Please see this previous answer for an overview, and this answer diving into the struggle to contain the slave trade throughout the Spanish Empire.

Also check out this online exhibit from the Smithsonian called The Other Slavery with several great talks presented by the leaders in the field.

Theres a few things to understand with this. First, American Indians were enslaved. Speaking as a historian of middle North America (Louisiana Territory) the American Indians were enslaved during the first approximately 150 years of French and Spanish colonies. However, in the Louisiana Colony, the enslavement of American Indians ended in the 1760s/1770s. This is due to the centrality of the fur trade and the essential role the American Indians had in that exchange. Enslaving the indigenous people made it difficult (duh) to maintain a positive relationship with them and they could not rely on them for profit.

Second, Europeans had been relying on African slave labor since before Columbus' voyages. Also, the slave trade was highly profitable. Slave traders were quite wealthy. A healthy, working-age Male could easily pull $1800 or more (approximately 4 months wages). Then there was the profitability slaves brought. Slaves were THE MOST valuable "piece of property" an American business owner/farmer owned. Theres a reason theres fugitive slave provisions in the Constitution. Theres a reason in the 1850s they made it legal to send bounty hunters across state lines to capture slaves. That's how valuable they were. But also shows how important it was to the American mindset (post colonial) that slaves be kept under their thumb and in a place of fear.