What system was created because of the decline in native population in South America?

a historian who compares the expansion of political systems to the expansion of economic systems to the expansion of economic systems is organizing history by theme.

hope this : d

after the spaniards introduced horses to plains native americans, the lives of the tribes changed. tribes became less settled and sedentary. the horse allowed them to hunt animals such as bison or buffalo, and, instead of staying in one place, tribes began to be nomadic.