James K Polk was President during the Mexican War. He also solved the boundary dispute in Oregon with Great Britian. Because of him, the United States added another 1/4-1/3 of territory. It also meant the end of Mexico as a potential rival in North America, thus pretty much guaranteeing that the US would be the dominant force in the Western Hemisphere. He was also a very hard worker. He is said to have accomplished more in his 1 term than any other President. He would often work late into the night. He decided not to run for another term because he had accomplished everything he wanted to. You'll notice that among the Great and Near Great, he's the only one that didn't serve another term.What was James Polk known for? He is often one of the forgetten Presidents when people try to name them.