Final answer:
The Appalachian Mountains were the western settlement boundary for the colonies, and the number of colonists per square mile varied across the region.
Step-by-step explanation:
The Appalachian Mountains were declared the western settlement boundary for the thirteen North American colonies by the Proclamation Line of 1763. This line was intended to prevent conflict with the French and Native Americans and to avoid the costs of defending the frontier. As for the number of colonists per square mile across most of the region, it is difficult to provide an exact figure as it varied depending on the specific area. However, it is important to note that the Appalachian Mountains acted as a somewhat permeable barrier to migration and diffusion.
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