Final answer:
King George III's establishment of the Appalachians as the western boundary of the colonies, through the Proclamation Line of 1763, was meant for strategic defense and to manage post-war economic challenges. The move was seen as tyrannical by the colonists who expected to expand into these lands as a reward for their participation in the French and Indian War.
Step-by-step explanation:
King George III made the Appalachians the western boundary of the colonists primarily for strategic defense and economic reasons. The Proclamation Line of 1763 was established after Britain's victory in the French and Indian War, which financially burdened the empire. The goals were to preempt conflict with Native Americans and the French in that region, manage the costs of defending new and distant frontiers, ensure easier collection of taxes, and enforce imperial laws. Despite these measures, the colonies viewed the act as an obstruction to their right to expand and as a form of tyranny especially because some colonists had received land grants west of the Appalachians and the colonists expected to be rewarded with access to these lands after the war.