Answer:
The Appalachian Mountains
Step-by-step explanation:
The Appalachians were a barrier to the westward expansion. It runs from southeastern Canada to central Alabama and was the physical boundary that prevented the westward settlement. The government-sponsored Daniel Boone to navigate a path to the rich lands beyond the mountains. After that, they were able to reach a path through the Cumberland Gap, that ran for 800 miles from Cumberland, Maryland to Vandalia Illinois.