Final answer:
The primary purpose of the Proclamation of 1763 was to prevent conflicts with Native American tribes by restricting colonial expansion west of the Appalachian Mountains.
Step-by-step explanation:
The main reason the British Parliament issued the Proclamation of 1763 was to pacify the Native American tribes and avoid conflict by controlling colonial expansion. The Proclamation established the Appalachian Mountains as the western boundary of colonial settlement to prevent settlers from moving into Native American territories, which could have resulted in further clashes. It was a response to both the costly Seven Years' War and the desire to maintain peaceable relations with the Native American tribes who lived beyond that line. Moreover, the British intended to manage the expansion and control the fur trade by allowing only licensed traders to operate beyond the boundary.