American Westward Expansion By Star1234 Apr 27, 1803 Louisiana Purchase Period: Jan 1, 1812 to Dec 31, 1860 American Westward Expansion May 17, 1819 Florida Cession May 12, 1845 Texas Annexation Apr 17, 1846 Gained Oregon County Jul 27, 1848 Mexican Cession Feb 15, 1853 Gadsen Purchase