Answer:
The Great Plains
Explanation:
The Great Plains is a vast prairie area east of the Rockies in the United States and Canada. The plains extend to the states of New Mexico, Texas, Oklahoma, Colorado, Kansas, Nebraska, Wyoming, Montana, South Dakota and North Dakota in the United States, and the provinces of Alberta, Manitoba and Saskatchewan in Canada. As it was a very wide area of land completely uninhabited in colonial times, it was a challenge to American expansion to the west. i hope this helps :)
