Frederick Jackson Turner, an American historian, produced the so-called "Turner Thesis" in 1893. Census records had shown that as of 1890, the frontier had officially closed, and, to Turner's mind, this marked the end of an era. He believed that the frontier was an integral part of American democracy, as it allowed pioneers to reinvent themselves and to gain access to a new beginning. The closing of the frontier troubled him, as he thought that Americans would not have access to continually new beginnings. The ability of Americans to reinvent themselves was part of the egalitarian American spirit. Turner's thesis played a role in fostering imperialism, as Americans believed that they had to expand abroad to find new frontiers. His thesis has been criticized for ignoring the reality that many people on the Western frontier experienced economic hardships and for ignoring the reality that Native Americans, Latinos, and other groups lived on the lands that were regarded as virgin territories by white Americans.

To Frederick Jackson Turner, the settlement of the West was a good thing and a bad thing.  The process of settling it was good, but the fact that the West became settled was bad for the United States.

To Turner, the existence of a frontier was basic to the American character.  Turner believed that Americans' basic character was formed by the fact that they had always been able to go out and "conquer" some new area of land.  This allowed Americans to be independent and and allowed democracy to flourish.  It allowed them to be ingenious and resourceful, which helped the US economy.

This meant that the "closing" of the West was bad news.  If there was no longer a frontier, how would Americans challenge themselves?  How would they maintain their independent and resourceful spirits?  These were serious problems in Turner's mind.