Final answer:
The Appalachian Mountains served as the natural boundary that confined English settlers to the eastern shore.
Step-by-step explanation:
The natural boundary that kept English settlers confined to the eastern shore was the Appalachian Mountains. After the French and Indian War, Britain issued the Proclamation Line of 1763, which declared the Appalachians as the western settlement boundary for the thirteen North American colonies. The purpose of the proclamation was to prevent further conflicts with the French and Native Americans and to avoid the cost of defending the frontier. The colonists, however, disregarded the proclamation and viewed it as tyranny.
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