"The North American continent as largely an unknown wilderness, to European eyes as remote as the moon…. . The English colonies were still confined between the Allegheny mountain chain and the Atlantic, a ribbon of settlement two thousand miles long and at most a tenth as wide." [Source: The Path Of Destiny by Thomas H. Raddall]
The Library of Congress site explained that The Proclamation of 1763, declared by the British after the French and Indian War, prohibited further American settlement west of the Appalachian Mountains and was intended to conciliate Native Americans by stopping encroachment on their lands.