I would say that one assumption is the superiority of Europeans over Africans: their belief that somehow they had the right to enslave other people.
This could be connected to their racism (they thought the same of native Americans and there was a discussion whether native Americans have souls) or religious feeling of superiority ("pagans are not the same as Christians"...)
"extolled" means to praise some thing highly.
Answer:
The American-Indian Wars were a centuries-long series of battles, ... the Native Americans (or Indians) who had thrived on the land for thousands of years. ... The fierce fighting started over territory and fur trade dominance ... Although they had already begun peace negotiations with the U.S. government.
NAFTA was signed on 17th December 1992 by all three members (Mexico, US, Canada) in their respective capitals and it came to power on January 1, 1994.
