When in 1890 the Superintendent of the census declared the American frontier closed, it meant there would no longer be a census report on the westward movement.
Three years later Frederick Jackson Turner wrote his famous paper on The Significance of the Frontier in American History. It was one of the most influential essays ever written by an American historian. In it he says that the frontier period decisively determined American character and institutions. His thesis in a nutshell was this: The existence of an area of free land, its continuous recession, and the advance of American settlement westward explain American development.
He proclaimed that this unique relationship of settlers and their environment was the central determining factor in American history. The two leading elements in this relationship were, first, the existence of free land, a constantly available territory into which settlers were free to enter and, second, the settlers' adaption to primitive conditions of life, involving a reversion to primitive social organization, followed by a process of development to civilized complexity again.
This pattern of reversion to primitive simplicity, followed by evolution to a civilized stage, was repeated on each new frontier in a 'perennial rebirth' and decisively determined American political and social attitudes and institutions. It made Americans egalitarian, independent, and individualistic and was the main source of American democracy. In fact, it was the settler who transformed the wilderness into a new social form, that is American and not European. Turner also broke down the frontier into the trader's, the rancher's, the miner's and the farmer's frontiers which all had different characters and effects. He saw, e.g. the fur trader as the first pioneer of civilization, transforming the Indians into nonprimitives. He saw the trader's trails and trading posts as the germs of our present highways and cities. And he concluded that the repeated frontier experience, shared in common by persons of all origins, was the true melting pot that made Americans into one people.