Colonists considered the area from the Appalachians to the Mississippi River as the "West" because it was the furthest western region of the colonies at that time. This area represented uncharted territory and unknown frontiers, offering new opportunities for settlement, economic ventures, and expansion. The Appalachians were seen as a natural boundary, separating the settled eastern regions from the untamed lands beyond. Additionally, the Mississippi River was a significant geographical landmark that marked the limits of colonial control and knowledge. Thus, the colonists considered this vast expanse of land as the "West" because it represented the westernmost edge of their known world.
Short answer
Colonists considered the area from the Appalachians to the Mississippi River as the "West" because it was the furthest western region of the colonies at that time and represented uncharted territory and new opportunities for settlement and expansion.
