The correct answer is D. Kept people from settling farther west
Step-by-step explanation:
In the United States, the Appalachian Mountains extend from the North of Maine to Alabama; this geographical feature creates a natural barrier that separates the East coast from western territories. Indeed, during the first decades of colonization, settlers only settled east to the Appalachian and in this territory, the first thirteen colonies were formed. This is because it was challenging to cross the Appalachian Mountains and settled in western territories. This means, these mountains initially prevented settlers from going farther west (option D.)