What was the key reason for the ending of the native civilizations of america?

the answer to fill in the blank in this question would be the word resource, it is defined as the money, material or people (since human resource is a very valuable good) that a company or a person has at disposition (meaning they can use the resource as they see fit), to be able to complete a task or achieve a goal.  

"a government in which power is divided between state and national levels". federalism is a system of government in which entities such and state and province, share power with the national government.