What concept did Frederick Jackson Turner emphasize regarding American expansion?

Frederick Jackson Turner emphasized the Frontier Thesis, which posits that the American frontier played a crucial role in shaping the nation's character, democracy, and societal development. In his famous essay presented in 1893, Turner argued that the availability of land and the process of westward expansion were fundamental to the growth of American individualism and innovation. He suggested that the frontier served as a "safety valve" for social pressures and economic difficulties, allowing individuals to seek new opportunities and forge a distinct American identity.

Turner's thesis also suggested that the closing of the frontier in the late 19th century marked the end of a significant period in American history, which could lead to a potential crisis in national character. This concept is fundamental to understanding American attitudes towards expansion and its implications for national identity, making it a cornerstone of historiographical discussions surrounding U.S. imperialism and expansionism.