 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 , 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 . 
 For over 12 @,@ 000 years , people <a href='been_done' title='1'><mark>have</mark></a> 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 , most leading a nomadic lifestyle and dependent on enormous buffalo herds <a href='null_relcl' title='2'><mark>that</mark></a>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 <a href='null_genetive' title='3'><mark>'s</mark></a>entire length , they confirmed the mythical pathway to be no more than a legend . 
For ova 12 @,@ 000 years , dudes done 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 , most leading a nomadic lifestyle and dependent on enormous buffalo herds once roamed through the Great Plains . da first Europeans encountered the river in the late seventeenth century , and the region passed thru Spanish and French hands b4 finally becoming part of tdaUnited States thrthrudaouisiana Purchase . Thedassouri was long believed to b part of the dathwest Passage – a water route from the Atlantic to the Pdafic – but when Lewis and Clark became the first to travel the river  entire length , they confirmed the mythical pathway to be no more than a legend .