The
Illini Confederacy once dominated what is today the St. Louis area. During the 17th century, the population of indigenous peoples in the area was well over tens of thousands, including 20,000 in the Grand Village of Illinois. Indigenous peoples in the area built earthwork mounds on both sides of the
Mississippi River, with the
Cahokia Mounds as the regional center. St. Louis would later receive the nickname of "Mound City".
Pierre Laclede Liguest and his 13-year-old grandson,
Auguste Chouteau, selected St. Louis as the site for a French fur trading post in 1764 because it was a rarely flooded area at the confluence of the Mississippi and Missouri Rivers. In 1770, ownership of St. Louis was transferred to Spain, and then returned to France during a secret treaty (
Treaty of San Ildefonso). The area became part of the United States in the 1803
Louisiana Purchase, and steadily grew thereafter. It was the starting point for
Lewis and Clark. St. Louis was incorporated as a city in 1823. Between 1840 and 1860, the population exploded, particularly because of the arrival of German and Irish immigrants. St. Louis's current boundaries were established in 1876. After the
American Civil War, St. Louis continued to grow into a major manufacturing center due to its access to rail and water transportation. By the 1890s, St. Louis was the 4th-largest city in the United States. In 1904, St. Louis hosted the
world's fair in
Forest Park and the Olympics at
Washington University's Francis Field. More than 20 million people visited the city during the fair's seven-month long run. St. Louis was seen as a city of industrialization with ties to the automobile industry. The
Great Migration between World War I and World War II brought thousands of African Americans to the city, boosting St. Louis's population to 800,000 by 1940. The population peaked in 1950 at 856,000. There was no more room for expansion within city boundaries and earlier immigrant generations started moving to suburbs that could not be annexed. During the mid-1960s, construction began on the
Gateway Arch and
Busch Stadium, in part to help revitalize the central business district. A 30-year downtown building boom followed. Today, there is a continued population decline although revitalization efforts are under way. ==Political divisions in Greater St. Louis==