Frederick Jackson Turner (1861-1932) was an American historian best known for his book, The Significance of the Frontier in American History, in which he presented his "Frontier Thesis." This central thesis was that the vitality of the American spirit rested on westward expansion.
Turner, who was chosen to speak in Chicago during the 1893 World's Columbian Exposition, told his audience that all the land in the American western frontier had been explored and settled, and the great era of expansion appeared to be over. He assured his audience, however, that expansion could continue as long as the U.S. broadened its notion of "manifest destiny" and looked beyond its continental borders toward the rest of the world. This message was of great importance to a nation that was increasingly coming to value imperial expansion.