 The Missouri River 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 <unk> as trappers explored the region and blazed trails . Pioneers headed west en <unk> 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 . 
