Louisiana Purchase in the context of "Adams–Onís Treaty"

St. Louis (/seɪnt ˈluːɪs, sənt-/ saynt LOO-iss, sənt-, sometimes referred to as St. Louis City, Saint Louis or STL) is an independent city in the U.S. state of Missouri. It lies near the confluence of the Mississippi and the Missouri rivers. In 2020, the city proper had a population of 301,578, while its metropolitan area, which extends into Illinois, had an estimated population of over 2.8 million. It is the largest metropolitan area in Missouri and the second-largest in Illinois. The city's combined statistical area is the 20th-largest in the United States.

The land that became St. Louis had been occupied by Native American cultures for thousands of years before European settlement. The city was founded on February 14, 1764, by French fur traders Gilbert Antoine de St. Maxent, Pierre Laclède, and Auguste Chouteau. They named it for King Louis IX of France, and it quickly became the regional center of the French Illinois Country. In 1804, the United States acquired St. Louis as part of the Louisiana Purchase. In the 19th century, St. Louis developed as 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 political boundaries. In 1904, it hosted the Louisiana Purchase Exposition, also known as the St. Louis World's Fair, and the Summer Olympics.

The French colonial empire (French: Empire colonial français) consisted of the overseas colonies, protectorates, and mandate territories that came under French rule from the 16th century onward. A distinction is generally made between the "First French colonial empire", that existed until 1814, by which time most of it had been lost or sold, and the "Second French colonial empire", which began with the conquest of Algiers in 1830. On the eve of World War I, France's colonial empire was the second-largest in the world after the British Empire.

France began to establish colonies in the Americas, the Caribbean, and India in the 16th century but lost most of its possessions after its defeat in the Seven Years' War. The North American possessions were lost to Britain and Spain, but Spain later returned Louisiana to France in 1800. The territory was then sold to the United States in 1803. France rebuilt a new empire mostly after 1850, concentrating chiefly in Africa as well as Indochina and the South Pacific. As it developed, the new French empire took on roles of trade with the metropole, supplying raw materials and purchasing manufactured items. Especially after the disastrous Franco-Prussian War, which saw Germany become the leading economic and military power of the continent of Europe, acquiring colonies and rebuilding an empire was seen as a way to restore French prestige in the world. It was also to provide manpower during the world wars.

Napoleon Bonaparte (born Napoleone di Buonaparte; 15 August 1769 – 5 May 1821), later known by his regnal name Napoleon I, was a French general and statesman who rose to prominence during the French Revolution and led a series of military campaigns across Europe during the French Revolutionary and Napoleonic Wars from 1796 to 1815. He led the French Republic as First Consul from 1799 to 1804, then ruled the French Empire as Emperor of the French from 1804 to 1814, and briefly again in 1815. He was King of Italy from 1805 to 1814, Protector of the Confederation of the Rhine from 1806 to 1813, and Mediator of the Swiss Confederation from 1803 to 1813.

Born on the island of Corsica to a family of Italian origin, Napoleon moved to mainland France in 1779 and was commissioned as an officer in the French Royal Army in 1785. He supported the French Revolution in 1789 and promoted its cause in Corsica. He rose rapidly through the ranks after winning the siege of Toulon in 1793 and defeating royalist insurgents in Paris on 13 Vendémiaire in 1795. In 1796, he commanded a military campaign against the Austrians and their Italian allies in the War of the First Coalition, scoring decisive victories and becoming a national hero. He led an invasion of Egypt and Syria in 1798, which served as a springboard to political power. In November 1799, Napoleon engineered the Coup of 18 Brumaire against the French Directory and became First Consul of the Republic. He won the Battle of Marengo in 1800, which secured France's victory in the War of the Second Coalition, and in 1803, he sold the territory of Louisiana to the United States. In December 1804, Napoleon crowned himself Emperor of the French, further expanding his power.

Missouri (see pronunciation) is a landlocked state in the Midwestern region of the United States. Ranking 21st in land area, it borders Iowa to the north, Illinois, Kentucky and Tennessee to the east, Arkansas to the south and Oklahoma, Kansas, and Nebraska to the west. In the south are the Ozarks, a forested highland, providing timber, minerals, and recreation. At 1.5 billion years old, the St. Francois Mountains are among the oldest in the world. The Missouri River, after which the state is named, flows through the center and into the Mississippi River, which forms the eastern border. With over six million residents, it is the 19th-most populous state of the country. The largest urban areas are St. Louis, Kansas City, Springfield, and Columbia. The capital is Jefferson City.

Humans have inhabited present-day Missouri for at least 12,000 years. The Mississippian culture, which emerged in the ninth century, built cities with pyramidal and other ceremonial mounds before declining in the 14th century. The Indigenous Osage and Missouria nations inhabited the area when European people arrived in the 17th century. The French incorporated the territory into Louisiana, founding Ste. Genevieve in 1735 and St. Louis in 1764. After a brief period of Spanish rule, the United States acquired Missouri as part of the Louisiana Purchase in 1803. Americans from the Upland South rushed into the new Missouri Territory, taking advantage of its productive agricultural plains; Missouri played a central role in the westward expansion of the United States. Missouri was admitted as a slave state as part of the Missouri Compromise of 1820. As a border state, Missouri's role in the American Civil War was complex, and it was subject to rival governments, raids, and guerilla warfare. After the war, both Greater St. Louis and the Kansas City metropolitan area became large centers of industrialization and business.

The Missouri River is a river in the Central and Mountain West regions of the United States. The nation's longest, it rises in the eastern Centennial Mountains of the Bitterroot Range of the Rocky Mountains of southwestern Montana, then flows east and south for 2,341 miles (3,767 km) before entering the Mississippi River north of St. Louis, Missouri. The river drains semi-arid watershed of more than 500,000 square miles (1,300,000 km), which includes parts of ten U.S. states and two Canadian provinces. Although a tributary of the Mississippi, the Missouri River is slightly longer and carries a comparable volume of water, though a fellow tributary (Ohio River) carries more water. When combined with the lower Mississippi River, it forms the world's fourth-longest river system.

For over 12,000 years, people have depended on the Missouri River and its tributaries as a source of sustenance and transportation. More than ten major groups of Native Americans populated the watershed, with most leading a nomadic lifestyle and dependent on enormous bison herds that roamed through the Great Plains. The first Europeans encountered the river in the late seventeenth century, and the region passed through Spanish and French hands before becoming part of the United States through the Louisiana Purchase.

St. Louis County is located in eastern Missouri. It is bounded by the City of St. Louis and the Mississippi River to the east, the Missouri River to the north, and the Meramec River to the south. As of the 2020 census, the population was 1,004,125, making it the most populous county in Missouri, and was estimated to be 987,059 in 2023. Its county seat is Clayton. The county is included in the St. Louis, MO–IL metropolitan statistical area.

After Great Britain took over former French territory east of the Mississippi River, many ethnic French colonists moved west. They settled the area of St. Louis County and founded the city of St. Louis in the late 1700s. The US acquired this territory in 1803 with the Louisiana Purchase.

The Kansas–Nebraska Act of 1854 (10 Stat. 277) was a territorial organic act that created the territories of Kansas and Nebraska. It was drafted by Democratic Senator Stephen A. Douglas, passed by the 33rd United States Congress, and signed into law by President Franklin Pierce. Douglas introduced the bill intending to open up new lands to develop and facilitate the construction of a transcontinental railroad. However, the Kansas–Nebraska Act effectively repealed the Missouri Compromise of 1820, stoking national tensions over slavery and contributing to a series of armed conflicts known as "Bleeding Kansas".

The United States had acquired vast amounts of land in the 1803 Louisiana Purchase, and since the 1840s, Douglas had sought to establish a territorial government in a portion of the Louisiana Purchase that was still unorganized. Douglas's efforts were stymied by Senator David Rice Atchison of Missouri and other Southern leaders who refused to allow the creation of territories that banned slavery; slavery would have been banned because the Missouri Compromise outlawed slavery in the territory north of latitude 36° 30′ north (except for Missouri). To win the support of Southerners like Atchison, Pierce and Douglas agreed to back the repeal of the Missouri Compromise, with the status of slavery instead decided based on "popular sovereignty". Under popular sovereignty, the citizens of each territory, rather than Congress, would determine whether slavery would be allowed.

The United States of America was formed after thirteen British colonies in North America declared independence from the British Empire on July 4, 1776. In the Lee Resolution, passed by the Second Continental Congress two days prior, the colonies resolved that they were free and independent states. The union was formalized in the Articles of Confederation, which came into force on March 1, 1781, after being ratified by all 13 states. Their independence was recognized by Great Britain in the Treaty of Paris of 1783, which concluded the American Revolutionary War. This effectively doubled the size of the colonies, now able to stretch west past the Proclamation Line to the Mississippi River. This land was organized into territories and then states, though there remained some conflict with the sea-to-sea grants claimed by some of the original colonies. In time, these grants were ceded to the federal government.

The first great expansion of the country came with the Louisiana Purchase of 1803, which doubled the country's territory, although the southeastern border with Spanish Florida was the subject of much dispute until it and Spanish claims to the Oregon Country were ceded to the US in 1821. The Oregon Country gave the United States access to the Pacific Ocean, though it was shared for a time with the United Kingdom. The annexation of the Republic of Texas in 1845 led directly to the Mexican–American War, after which the victorious United States obtained the northern half of Mexico's territory, including what was quickly made the state of California.