TrackingWriters, HistoryOf. "The existence of an area of free land, its continuous recession, and the advance of American settlement westward explain American development." * FrancisParkman * TheodoreRoosevelt * AmericanNationalism * [http://www.pbs.org/weta/thewest/people/s_z/turner.htm PBS - THE WEST] http://www.pbs.org/weta/thewest/people/images/turner.jpg