Answer:
To stop the colonists moving beyond the Appalachian mountain.
Step-by-step explanation:
King George III of England issued the proclamation act in 1763 after the French and Indian War in America. After the war, along with the victory of British, the colonists in the 13 colonies were spreading towards the West. British closed down expansion towards westward beyond Appalachia. By stopping colonists, it strengthens the British empire economy and official relations with native Indians.