Why did they want to move natives to the Great Plains

The rationale was that moving Native Americans to this Permanent Indian Frontier would open up land in the eastern United States for European American settlers, while protecting them until such time as they were willing and able to assimilate into American society. Jefferson also believed that consolidating Native Americans in the Great Plains would create a barrier that would prevent American settlers from dispersing too widely.

yellow fever and other tropical diseases

try this

explanation: