James K. Polk (1795–1849), the eleventh president, led the United States during the Mexican-American War. Polk began his career as a lawyer before being elected to the Tennessee legislature in 1823. In Tennessee Polk became a close associate of Andrew Jackson, and he went on to serve in the US House of Representatives from 1825 to 1839, and then as governor of Tennessee from 1839 to 1841. In 1844, Polk improbably beat out Martin Van Buren, James Buchanan, and Lewis Cass for the Democratic nomination for president. He won the election over...