The administration of James Knox Polk (1795-1849), eleventh president of the United States, saw America at war with Mexico. As a consequence, Polk added more territory to the United States than had any other president except Thomas Jefferson.

James K. Polk was born on Nov. 2, 1795, in Mecklenburg County, North Carolina. As a child, he moved to an area in Tennessee settled by his grandfather, a land speculator. After graduation from the University of North Carolina in 1818, he studied law under Congressman Felix Grundy and was admitted to the bar in 1820. Elected to the legislature in 1822, Polk became known as an opponent of the state's banks and land speculators. He supported Andrew Jackson, who was an old friend of his father, for the presidency in the election of 1824.

As a Jacksonian, Polk was elected to the U.S. House of Representatives in 1825, becoming a leader of his party. He...