Final answer:
Great Plains tribes were expert horse riders and buffalo hunters, whose nomadic lifestyle emerged because of the reintroduction of the horse to North America.
Step-by-step explanation:
According to the sources, the Great Plains tribes are best described as Expert horse riders and buffalo hunters.
The transformation of Plains groups from agriculturalists to nomadic hunter/gatherers occurred in part because of the reintroduction of the horse to North America.
This event drastically altered the lifestyle of many groups like the Sioux, Crow, Cheyenne, and Comanche, who began utilizing horses to follow and hunt the great bison herds more effectively, marking a significant shift in their culture and social organization.