The Mississippi River is the chief river of the largest drainage system in North America.Flowing entirely in the United States (though its drainage basin reaches into Canada), it rises in northern Minnesota and meanders slowly southwards for 2,340 miles (3,770 km) to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watersheddrains all or parts of 31 US states and 2 Canadian provinces between the Rocky and Appalachian Mountains. The Mississippi ranks as the fourth longest and tenth largest river in the world. The river either borders or cuts through the states ofMinnesota, Wisconsin, Iowa, Illinois, Missouri,Kentucky, Tennessee, Arkansas, Mississippi, andLouisiana.
Native Americans long lived along the Mississippi and its tributaries. Most were hunter-gatherers or herders, but some, such as the Mound builders, formed prolific agricultural societies. The arrival of Europeans in the 1500s changed the native way of life as first explorers, then settlers, ventured into the basin in increasing numbers. The river served first as a barrier – forming borders for New Spain, New France, and the early United States – then as a vital transportation artery and communications link. In the 19th century, during the height of Manifest Destiny, the Mississippi and several western tributaries, most notably the Missouri, formed pathways for the western expansion of the United States.
Formed from thick layers of this river's silt deposits, the Mississippi River Valley is one of the most fertile agricultural regions of the country, which resulted in the river's storied steamboat era. During theAmerican Civil War, the Mississippi's capture byUnion forces marked a turning point towards victory because of the river's importance as a route of trade and travel, not least to the Confederacy. Because of substantial growth of cities and the larger ships andbarges that supplanted riverboats, the decades following the 1900s saw the construction of massiveengineering works such as levees, locks and dams, often built in combination.
Since modern development of the basin began, the Mississippi has also seen its share of pollution and environmental problems – most notably large volumes of agricultural runoff, which has led to theGulf of Mexico dead zone off the Delta. In recent years, the river has shown a steady shift towards theAtchafalaya River channel in the Delta; a course change would prove disastrous to seaports such asNew Orleans. While a system of dikes and gates has held the Mississippi in its current channel to date, the shift becomes more likely each year due tofluvial processes
For over 12,000 years, people have depended on the Missouri and its tributaries as a source of sustenance and transportation. More than ten major groups of Native Americans populated the watershed, most leading a nomadic lifestyle and dependent on enormous buffalo herds that once 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 finally becoming part of the United States through the Louisiana Purchase. The Missouri was long believed to be part of the Northwest Passage – a water route from the Atlantic to the Pacific – but when Lewis and Clark became the first to travel the river's entire length, they confirmed the mythical pathway to be no more than a legend.
The Missouri was one of the main routes for the westward expansion of the United States during the 19th century. The growth of the fur trade in the early 1800s laid much of the groundwork as trappers explored the region and blazed trails. Pioneersheaded west en masse beginning in the 1830s, first by covered wagon, then by the growing numbers of steamboats entering service on the river. Former Native American lands in the watershed were taken over by settlers, leading to some of the most longstanding and violent wars against indigenous peoples in American history.
During the 20th century, the Missouri River basin was extensively developed for irrigation, flood control and the generation of hydroelectric power. Fifteen dams impound the main stem of the river, with hundreds more on tributaries. Meanders have been cut and the river channelized to improve navigation, reducing its length by almost 200 miles (320 km) from pre-development times. Although the lower Missouri valley is now a populous and highly productive agricultural and industrial region, heavy development has taken its toll on wildlife and fish populations as well as water quality.