But with all these similarities there are essential differences, due to the place element and the time element. It is evident that the farming frontier of the Mississippi Valley presents different conditions from the mining frontier of the Rocky Mountains. The frontier reached by the Pacific Railroad, surveyed into rectangles, guarded by the United States Army, and recruited by the daily immigrant ship, moves forward at a swifter pace and in a different way than the frontier reached by the birch canoe or the pack horse. The geologist traces patiently the shores of ancient seas, maps their areas, and compares the older and the newer. It would be a work worth the historian’s labors to mark these various frontiers and in detail compare one with another. Not only would there result a more adequate conception of American development and characteristics, but invaluable additions would be made to the history of society.
Historian Frederick Jackson Turner presented his “frontier thesis” in an address in Chicago, the site of the 1893 World’s Columbian Exposition. Turner pointed to expansion as the most important factor in American history. He claimed that “the existence of an area of free land, its continuous recession, and the advance of American settlement westward explain American development.” In 1890, however, the Census Bureau stated that all the land within the United States was claimed, and there was no longer a frontier. “Now, four centuries from the discovery of America, at the end of a hundred years of life under the Constitution, the frontier has gone, and with its going has closed the first period of American history,” Turner asserted, questioning how American culture and history would develop and whether Americans would retain “that coarseness and strength combined with acuteness and acquisitiveness . . . that dominant individualism” bred by expansion now that the frontier was closed.