Influence on history

For a century, the Appalachians were a barrier to the westward expansion of the British colonies. The continuity of the mountain system, the bewildering multiplicity of its succeeding ridges, the tortuous courses and roughness of its transverse passes, a heavy forest, and dense undergrowth all conspired to hold the settlers on the seaward-sloping plateaus and coastal plains. Only by way of the Hudson and Mohawk Valleys, Cumberland Gap, the Wachesa Trail,[undue weight? – discuss] and round about the southern termination of the system were there easy routes to the interior of the country, and these were long closed by powerful Native American tribes such as the Iroquois, Creek, and Cherokee, among others. Expansion was also blocked by the alliances the British Empire had forged with Native American tribes, the proximity of the Spanish colonies in the south and French activity throughout the interior.

Oil painting of Daniel Boone escorting settlers through the Cumberland Gap

In eastern Pennsylvania the Great Appalachian Valley, or Great Valley, was accessible by reason of a broad gateway between the end of South Mountain and the Highlands, and many Germans and Moravians settled here between the Susquehanna and Delaware Rivers forming the Pennsylvania Dutch community, some of whom even now speak a unique American dialect of German known as the "Pennsylvania German language" or "Pennsylvania Dutch." These latecomers to the New World were forced to the frontier to find cheap land. With their followers of both German, English and Scots-Irish origin, they worked their way southward and soon occupied all of the Shenandoah Valley, ceded by the Iroquois, and the upper reaches of the Great Valley tributaries of the Tennessee River, ceded by the Cherokee.

By 1755, the obstacle to westward expansion had been thus reduced by half; outposts of the English colonists had penetrated the Allegheny and Cumberland plateaus, threatening French monopoly in the transmontane region, and a conflict became inevitable. Making common cause against the French to determine the control of the Ohio valley, the unsuspected strength of the colonists was revealed, and the successful ending of the French and Indian War extended England's territory to the Mississippi. To this strength the geographic isolation enforced by the Appalachian mountains had been a prime contributor. The confinement of the colonies between an ocean and a mountain wall led to the fullest occupation of the coastal border of the continent, which was possible under existing conditions of agriculture, conducting to a community of purpose, a political and commercial solidarity, which would not otherwise have been developed. As early as 1700 it was possible to ride from Portland, Maine, to southern Virginia, sleeping each night at some considerable village. In contrast to this complete industrial occupation, the French territory was held by a small and very scattered population, its extent and openness adding materially to the difficulties of a disputed tenure. Bearing the brunt of this contest as they did, the colonies were undergoing preparation for the subsequent struggle with the home government. Unsupported by shipping, the American armies fought toward the sea with the mountains at their back protecting them against British leagued with the Native Americans. The few settlements beyond the Great Valley were free for self-defense because debarred from general participation in the conflict by reason of their position.

Before the French and Indian War, the Appalachian Mountains laid on the indeterminate boundary between Britain's colonies along the Atlantic and French areas centered in the Mississippi basin. After the French and Indian War, the Proclamation of 1763 restricted settlement for Great Britain's thirteen original colonies in North America to east of the summit line of the mountains (except in the northern regions where the Great Lakes formed the boundary). Although the line was adjusted several times to take frontier settlements into account and was impossible to enforce as law, it was strongly resented by backcountry settlers throughout the Appalachians. The Proclamation Line can be seen as one of the grievances which led to the American Revolutionary War. Many frontier settlers held that the defeat of the French opened the land west of the mountains to English settlement, only to find settlement barred by the British King's proclamation. The backcountry settlers who fought in the Illinois campaign of George Rogers Clark were motivated to secure their settlement of Kentucky.

With the formation of the United States, an important first phase of westward expansion in the late 18th century and early 19th century consisted of the migration of European-descended settlers westward across the mountains into the Ohio Valley through the Cumberland Gap and other mountain passes. The Erie Canal, finished in 1825, formed the first route through the Appalachians that was capable of large amounts of commerce.