Tomorrow is Juneteenth, a federal holiday enacted to commemorate June 19, 1865, the day when enslaved people in Galveston, Texas learned that they were free.
Here are two free resources to learn more about enslaved ancestors:

Enslaved: Peoples of the Historical Slave Trade is a searchable collection of 700,000 people and events pertaining to those who took part in slave trading, including the enslaved, their owners and those who profited from their suffering.
The second resource is SlaveVoyages.

SlaveVoyages tracks transatlantic AND domestic voyages in the United States that involved the transportation of enslaved persons.
There are names of 93,00 Africans in the database and is searchable.
To understand just how prolific the slave trade became, it’s worth a few moments to view the time lapse video of the slave ship routes beginning in 1660.
The 3D videos of slaving vessels which show the construction of the ships, villages in Africa from which the enslaved were taken and the route to North America.
Both of these websites offer valuable resources for genealogists, but also provide excellent learning experiences.
Thanks for mentioning these sites – I’ll add them to the Genealogy Toolbox on my library’s website and to my own (though it may take more time to get up there on the latter).