Final answer:
Colonists were upset by the Proclamation of 1763 because it restricted their anticipated opportunity to settle and access lands west of the Appalachian Mountains, which they believed would be available after the Seven Years' War. The Proclamation was seen as a betrayal and added to the tensions leading up to the American Revolution, causing many to ignore the edict.
Step-by-step explanation:
The Proclamation of 1763 emerged as a significant source of tension between Britain and its American colonies. Following the Seven Years' War, also known as the French and Indian War, British colonists were barred by the Proclamation from settling west of the Appalachian Mountains. This territory was designated as an Indian Reserve, in spite of colonial anticipation that the victory over France would lead to settlement opportunities in areas like the Ohio Valley.
Colonists were upset by the Proclamation for several reasons. They had hoped to move west to find new land and economic possibilities, especially as land in eastern territories grew scarce due to over-farming and lack of availability for the growing population. Landowners and speculators, including prominent figures like George Washington, had invested heavily in these lands, expecting to diversify and expand their holdings.
There was a strong belief among colonists that they had fought alongside British troops against the French and Native allies with the understanding that post-war, they would gain access to the western lands. When the British government instead prohibited settlement to maintain peace with Native tribes and to manage colonial governance more effectively, it was viewed as a betrayal and fueled colonial dissatisfaction with British rule. Thus, the Proclamation was widely disregarded and contributed to the growing movement for American independence.