Turner's frontier thesis, perhaps the most famous theory in American history, argued that the closing of the American frontier in the 1890 census, which stated that there no longer was a frontier boundary line in the US, marked the end of the first phase of United States' history. More importantly, this thesis argued that the frontier was the single defining element in the development of the US spirit or character. Turner described this character, formed he argued by the existence of a frontier wilderness into which white Americans could throw their energies and talents, as one of
strength combined with acuteness and acquisitiveness ... practical inventive turn of mind ... restless, nervous energy ... [and] dominant individualism.
Without the outlet of the frontier for restless individuals, Turner worried about what the future of the country would hold.
Most historians now reject Turner's thesis that conquering the frontier was the master narrative defining the US experience up until 1890. Historians argue that we are defined by slavery, the huge and successive waves of immigration that populated this country largely with Europeans, and/or the rise of a powerful industrial machine in the last half of the nineteenth century. Others argue that the various "frontiers" in the American experience are so disparate that they don't cohere into a meaningful whole.
Many historians argue that it was community, not individualism, that made survival possible in the frontier. Almost all historians today also reject the triumphalist narrative that the spread of white culture represented "progress" over "savagery" and point to the genocide and suffering frontier expansion cost native peoples, as well as women and Asians brought to the frontier.