<P> Control over North America (1750--2008) </P> <P> The 1783 Treaty of Paris with Great Britain defined the original borders of the United States . It generally stretched from the Eastern Seaboard to the Mississippi River in the west . There were ambiguities in the treaty regarding the exact border with Canada to the north that led to disputes that were resolved by the Webster--Ashburton Treaty in 1842 . Beginning in the late 18th century, the new nation organized areas west of the Original thirteen states into several United States territories, setting a template for future expansion . </P> <P> The Louisiana Purchase in 1803, was negotiated with Napoleon during the presidency of Thomas Jefferson; the territory was acquired from France for $15 million (equivalent to $245 million in present - day terms). A small portion of this land was ceded to Britain in 1818 in exchange for the Red River Basin . More of this land was ceded to Spain in 1819 with the Florida Purchase, but was later reacquired through Texas annexation and Mexican Cession . </P> <P> West Florida was declared to be a U.S. possession in 1810 by President James Madison after the territory had declared its independence from Spain . Madison ordered the U.S. Army to take control . Six weeks later, the army entered and occupied the capital, St. Francisville, putting an end to the republic after 74 days of independence . Spain did not relinquish its claim to sovereignty (see West Florida Controversy) until ratification of the Adams--Onís Treaty . General Andrew Jackson personally accepted the delivery of West Florida from its Spanish governor on July 17, 1821 . </P>

In the first half of the nineteenth century the united states gained the most territory through