In 1763, after Great Britain emerged triumphant from the Seven Years' War, it issued a Royal Proclamation that prohibited American colonists from settling west of the Appalachians. The British had found it difficult enough to administer its Eastern colonies; allowing settlement west of the Appalachians would have made life harder still, stretching the colonial administration's resources to breaking point. Furthermore, despite the British having prevailed in the recent conflict, threats still remained. The existence of French settlers and Native-American tribes west of the Appalachians meant that a new war could spark into life at any moment. So the last thing the British wanted was hordes of American colonists heading out west, potentially fueling French and native resentment.
On the whole, the American colonists were opposed to the Proclamation. They thought it ceded too much land to the defeated enemy and thwarted their long-held ambitions of territorial expansion. In any case, the Proclamation was virtually impossible to enforce. The British simply didn't have sufficient manpower or resources to be able to stop scores of settlers from heading out west to fulfill what they saw as their destiny. Officially, the British ignored the colonists' protests, but in actual fact the colonists were easily able to violate the terms of the Proclamation with impunity, buying up vast tracts of native land in the assurance that the Proclamation was just a temporary measure.