James Polk (1795-1849) served as the 11th U.S. president from 1845 to 1849. During his tenure, America’s territory grew by more than one-third and extended across the continent for the first time. Before his presidency, Polk served in the Tennessee legislature and the U.S. Congress; in 1839 he became governor of Tennessee. A Democrat who was relatively unknown outside of political circles, Polk won the 1844 presidential election as the dark horse candidate. As 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), in which the United States acquired California and much of the present-day Southwest. Polk kept his campaign promise to be a one-term president and did not seek reelection. Soon after leaving the White House, he died at age 53.