James K. Polk, our 11th President, returned the country to Jacksonian-Democratic rule. He is most famous for the Mexican War (of which Lincoln was an adamant critic) and his expansionist policy in general. For his biography, you'd be best served reading "A Country of Vast Designs" by Robert Merry.
James Knox Polk ( 1795-1849) was the 11th President of the United States (1845–1849). Polk was born in North Carolina. A Democrat, Polk served as the 17th Speaker of the House of Representatives (1835–1839) and Governor of Tennessee (1839–1841). Polk was the dark horse candidate for president in 1844, defeating Henry Clay of the rival Whig Party by promising to annex Texas. Polk was a leader of Jacksonian Democracy during the Second Party System.
Often referred to as the first "dark horse," James K. Polk was the 11th President of the United States from 1845 to 1849, the last strong President until the Civil War. Learn more: http://go.wh.gov/ASjP5T