The president who had those ideas was James K. Polk. When he was the president, he reduced tariffs, reformed the national banking system and settled a boundary dispute with the British that secured the Oregon Territory for the United States. Polk also led the nation into the Mexican-American War (1846-48), which the United States acquired California and much of the present-day southwest. It should also be mentioned that during his tenure, America's territory grew by more than one-third and extended across the continent for the first time.