James Knox Polk (November 2, 1795 – June 15, 1849) was the 11th president of the United States, serving from 1845 to 1849. He previously was the 13th Speaker of the House of Representatives (1835–1839) and ninth governor of Tennessee (1839–1841). A protégé of Andrew Jackson, he was a member of the Democratic Party and an advocate of Jacksonian democracy. Polk is chiefly known for extending the territory of the United States through the Mexican–American War; during his presidency, the United States expanded significantly with the annexation of the Republic of Texas, the Oregon Territory, and the Mexican Cession following American victory in the Mexican–American War.
After building a successful law practice in Tennessee, Polk was elected to its state legislature in 1823 and then to the United States House of Representatives in 1825, becoming a strong supporter of Andrew Jackson. After serving as chairman of the Ways and Means Committee, he became Speaker of the House in 1835, the only person to have served both as Speaker and U.S. president. Polk left Congress to run for governor of Tennessee, winning in 1839 but losing in 1841 and 1843. He was a dark horse candidate in the 1844 presidential election as the Democratic Party nominee; he entered his party's convention as a potential nominee for vice president but emerged as a compromise to head the ticket when no presidential candidate could secure the necessary two-thirds majority. In the general election, Polk defeated Henry Clay of the rival Whig Party.
Historians have praised Polk for meeting every major domestic and foreign policy goal he had set during his single term. After a negotiation fraught with the risk of war, he reached a settlement with Great Britain over the disputed Oregon Country, the territory, for the most part, being divided along the 49th parallel. He provoked a war with Mexico in an attempt to expand the United States and succeeded in doing so, as it resulted in Mexico's cession of nearly all the American Southwest. He secured a substantial reduction of tariff rates with the Walker tariff of 1846. The same year, he achieved his other major goal, re-establishment of the Independent Treasury system. True to his campaign pledge to serve only one term, Polk left office in 1849 and returned to Tennessee, where he died three months after leaving the White House.