<P> Mexican Cession lands were captured in the Mexican--American War in 1846--48, and ceded by Mexico in the Treaty of Guadalupe Hidalgo, where Mexico agreed to the present Mexico--United States border except for the later Gadsden Purchase . The United States paid $15 million (equivalent to $394 million in present - day terms) and agreed to pay claims made by American citizens against Mexico which amounted to more than $3 million (equivalent to $79 million today). </P> <P> In the Gadsden Purchase of 1853, the United States purchased a strip of land along the Mexico--United States border for $10 million (equivalent to $294 million in present - day terms), now in New Mexico and Arizona . The territory was also bought as Americans were passing through the land west to California . After the American Mexican War, over the dispute of border claims, American bought the land to prevent future conflict . Few historians would argue the territory was intended for a southern transcontinental railroad . </P> <P> Alaska Purchase from the Russian Empire for $7.2 million (2 cents per acre) on March 30, 1867 (equivalent to $126 million in present - day terms), as a vital refueling station for ships trading with Asia . The land went through several administrative changes before becoming an organized territory on May 11, 1912, and the 49th state of the U.S. on January 3, 1959 . </P> <Table> <Tr> <Td> <P> Hawaii and Outlying Islands </P> </Td> </Tr> <Tr> <Td> <Ul> <Li> <P> In 1959, 94% of Hawaii's residents voted to relinquish all land claims (proposition 2) to the United States and become a state . </P> </Li> <Li> <P> Today's United States Minor Outlying Islands excluding Caribbean </P> </Li> </Ul> </Td> </Tr> </Table>

Where was most of the territory the united states acquired during the era of westward expansion