President James K. Polk served as the 11th President of the United States from 1845 to 1849. He was a member of the Democratic Party and is known for his strong belief in Manifest Destiny, the idea that the U.S. was destined to expand across the North American continent. During his presidency, Polk oversaw significant territorial expansion, including the acquisition of Texas, the Oregon Territory, and the lands gained from the Mexican-American War. His administration is often credited with shaping the modern boundaries of the United States, but it also faced criticism for its role in the expansion of slavery.