Westward expansion was a key factor in the development of the United States. It gave the country access to vast amounts of natural resources, such as land, timber, and minerals, which helped fuel the country's economy. It also allowed the United States to expand its territory and become a continental power.
If westward expansion had not happened, the United States would likely be a much smaller country today. It would not have had access to the same resources or the same amount of territory. As a result, it would not have been able to develop into the economic and military superpower that it is today.