Before European settlement, the area was a regional center of Native American Mississippian culture. St. Louis was founded on February 14, 1764, by French fur traders Gilbert Antoine de St. Maxent, Pierre Laclède and Auguste Chouteau, who named it for Louis IX of France. In 1764, following France's defeat in the Seven Years' War, the area was ceded to Spain. In 1800, it was retroceded to France, which sold it three years later to the United States as part of the Louisiana Purchase; the city was then the point of embarkation for the Corps of Discovery on the Lewis and Clark Expedition. In the 19th century, St. Louis became a major port on the Mississippi River; from 1870 until the 1920 census, it was the fourth-largest city in the country. It separated from St. Louis County in 1877, becoming an independent city and limiting its own political boundaries. St. Louis had a brief run as a world-class city in the early 20th century. In 1904, it hosted the Louisiana Purchase Exposition and the Summer Olympics.