James Knox Polk was the 11th President of the United States, serving from 1845 to 1849. A member of the Democratic Party, he was born in North Carolina and later moved to Tennessee, where he began his political career. Polk is best known for his expansionist policies, which included the annexation of Texas and the Oregon Territory, significantly increasing the size of the United States. His presidency also included the Mexican-American War, which further shaped the nation's borders and identity.