It is difficult to discuss the influence of any national stock on American history without being involved in the larger question of which is the more important, environment or heredity. Naturally, to the American historian, environment is all important, and in the concept of the frontier developed by F. J Turner and others, the pioneer was wholly a child of the American continent. This view of the pioneer, however, originates less in history than in the eighteenth-century idea of a natural man. The real frontiersman was himself an immigrant or the child of immigrant parents, practising a European religion, and attempting to realize European ideals in a new country.
The Scotch-Irish were the dominant strain in the frontier population in all the colonies south of New York. Emigration from Ulster was as much a feature of American history in the eighteenth century as Irish catholic emigration in the next and had a much greater effect on the development of the country. From 1718, they had poured into America, mainly through Philadelphia, at the rate of about 4,000 a year. From there they made their way to the frontier and then down the lateral valleys of the Appalachians into the Valley of Virginia and piedmont North and South Carolina.