<P> The concept of expanding territorial control was popularized in the 19th century as the doctrine of Manifest Destiny and was realized through conquests such as the Mexican--American War of 1846, which resulted in the annexation of 525,000 square miles of Mexican territory . While the US government does not refer to itself as an empire, the continuing phenomenon has been acknowledged by mainstream Western writers including Max Boot, Arthur Schlesinger, and Niall Ferguson . </P> <P> Thomas Jefferson, in the 1790s, awaited the fall of the Spanish Empire "until our population can be sufficiently advanced to gain it from them piece by piece". In turn, historian Sidney Lens notes that "the urge for expansion--at the expense of other peoples--goes back to the beginnings of the United States itself". Yale historian Paul Kennedy put it, "From the time the first settlers arrived in Virginia from England and started moving westward, this was an imperial nation, a conquering nation ." Detailing George Washington's description of the early United States as an "infant empire", Benjamin Franklin's writing that "the Prince that acquires new Territory...removes the Natives to give his own People Room...may be properly called (Father) of (his) Nation", and Thomas Jefferson's statement that the United States "must be viewed as the nest from which all America, North & South is to be peopled", Noam Chomsky said that "the United States is the one country that exists, as far as I know, and ever has, that was founded as an empire explicitly". </P> <P> A national drive for territorial acquisition across the continent was popularized in the 19th century as the ideology of Manifest Destiny . It came to be realized with the Mexican--American War of 1846, which resulted in the annexation of 525,000 square miles of Mexican territory, stretching up to the Pacific coast . </P> <P> President James Monroe presented his famous doctrine for the western hemisphere in 1823 . Historians have observed that while the Monroe Doctrine contained a commitment to resist colonialism from Europe, it had some aggressive implications for American policy, since there were no limitations on the US's own actions mentioned within it . Scholar Jay Sexton notes that the tactics used to implement the doctrine were "modeled after those employed by British imperialists" in their territorial competition with Spain and France . Eminent historian William Appleman Williams dryly described it as "imperial anti-colonialism ." </P>

Us imperialism in the late 19th century was supported by which theory