American imperialism is the economic, military and cultural philosophy which states that the United States, either directly or indirectly, affects and controls other countries or their policies. Such influence is often closely associated with expansion into foreign territories. The concept of an American Empire was first popularised during the presidency of James K. Polk who led the United States into the Mexican–American War of 1846, and the eventual annexation of California and other western territories via the Treaty of Guadalupe Hidalgo and the Gadsden purchase. 

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 expansionat the expense of other peoplesgoes 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", Chomsky stated, "the United States is the one country that exists, as far as I know, and ever has, that was founded as an empire explicitly".
Was there conflict between 2 groups?
James K. Polk who led the United States into the Mexican–American War of 1846