<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> 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>
in the first half of the nineteenth century the united states gained the most territory through
in the first half of the nineteenth century the united states gained the most territory through
Louisiana Purchase
Louisiana Purchase