Answer:
The Appalachian Mountains
Step-by-step explanation:
For America, the Appalachian mountain played a crucial role as it opened the westward expansion. The Appalachian Mountains extend from Newfoundland in Canada to Alabama. The Appalachian mountains allowed settlement from the east to move to the west. The westward expansion allowed settlers to move in the west to claim the region for America and also assisted in the economy through farming and ranching.