Why did the policy of treating the great plains as a huge reservation change?

Policy of treating Great Plains as a huge reservation changes because white settlers began wanting land on the plains.  

Explanation:

Settlers are the one who migrate from the other area to that new one. Jamestown, Virginia was the place where first colony was established and many people settle there as they were persecuted by various regions in 1607. In '1770', more than '2 million' people settled to 13 northern American colonies. Because of more people settling there, reservation policy changed. 

It's lithogenous i believe of course i looked it up.

Master planned communities outside of chicago. note: population density means people living in an area per square mile. chicago, an urban and highly populated area has a much more higher density than a desert, amish community, settlement, or nomadic region.