The Appalachian Mountains were a physical barrier that prevented American colonists from settling west of the 13 original colonies during most of the 18th century. On the other side of the Appalachian Mountains were several different Native American tribes who already established their communities their.
Towards the middle of the 18th century, the American colonists began to develop the ability to travel west of these mountains, even though the British government forbid them to do so in the Proclamation of 1763. This had negative consequences, as white settlers struggled in their attempts to get pass these mountains and it caused tension between the British government and the colonists.
I believe the answer is: The mountains stopped expansion of the colonies
The terrain that exist in the mountains make it really hard for them to go over to create new colonies. Because of this, many settlers decided to stop their expansion on the mountain area and utilize the resources around to build various type of businesses (such as agricultural field, timber, farming, etc)
