14. James K. Polk
At age 49, James Polk was younger than any previous president when he entered the White House. A workaholic, America’s new chief executive set an ambitious agenda with four major goals: cut tariffs, reestablish an independent U.S. Treasury, secure the Oregon Territory and acquire the territories of California and New Mexico from Mexico. Polk eventually achieved all his goals. He was a champion of manifest destiny–the belief that the United States was fated to expand across the North American continent–and by the end of his four years in office, the nation extended, for the first time, from the Atlantic Ocean to the Pacific Ocean.