With its vast distances the West was peculiarly dependent on river transportation — at least until the coming of the railroads. Since the early 19th century, fur traders had floated their pelts down the natural highway of the Missouri and its tributaries to make St. Louis the great fur center of the nation. At the same time a hardy breed of rivermen poled and steered heavily-laden flatboats down the Mississippi to New Orleans, the early West’s great outlet. But such river traffic was largely one-way, and only when steamboats made it possible to travel upstream was western travel revolutionized. The two decades before the Civil War witnessed tremendous growth in steam navigation on the upper Mississippi, the Missouri, the Arkansas and the Red River of Texas. Overlanders to California and Oregon took steamboats up the Mississippi to St. Louis, then continued up the Missouri (the “Big Muddy”) to jumping off places like Independence. By 1860 steamboats had penetrated 2,200 miles up the Missouri’s winding course as far as Fort Benton in Montana, fostering a river trade that lasted until the 1880s when it lost out to the railroads.

In the wake of the Lewis and Clark expedition a succession of explorers, mainly U.S. army officers, surveyed and mapped large tracts of the Louisiana Purchase, the Rockies and the Pacific coast. The earliest was Zebulon M. Pike, whose first expedition (1805) failed to discover the source of the Mississippi, but whose second (1806-1807) took him to Colorado and to the headwaters of the Arkansas and Red rivers and across the closed border of the Spanish Southwest. Pike’s account of his travels did much to popularize the myth of the Plains as the “Great American Desert,” an impression confirmed by explorer Stephen H. Long after his expedition to the Rockies in 1820. But by the 1840s, a new sentiment had taken hold — that it was America’s “manifest destiny” to expand across the continent. The spirit of expansionism was fueled by the efforts of John C. Fremont who, guided by mountain-man Kit Carson, led expeditions to the Rockies (1842); over the Oregon Trail (1844); and into California (1845-1846), where he joined American settlers in the Bear Flag revolt against Mexican rule. Though Fremont discovered no new routes, and thus did not technically merit the nickname the “Pathfinder,” he gathered important geographical data and ignited popular interest in western settlement with his glowing reports.

Fueled by European demand for beaver hats, the North American trade that began with the French and English colonization of eastern North America moved West as supplies were trapped out. By the late 18th century, the North American trade was controlled by the Hudson’s Bay Company of Britain and the North West Company of Canada, but these were soon challenged by American entrepreneurs, newly awakened to the continent’s natural abundance by the Lewis and Clark expedition. Over the next 40 years, American companies like John Jacob Astor’s American Fur Company, Manuel Lisa’s Missouri Fur Company and William H. Ashley’s Rocky Mountain Fur Company, dominated the fur trade of the trans-Mississippi region. They built forts along the rivers of the West — the Missouri, Yellowstone, Green, Snake, Laramie and Platte — the forts serving as supply points and trading posts where trappers, traders and Indians engaged in commerce. The fur trade dwindled in the 1840s when silk “top” hats came into fashion, but the forts continued to play a vital role in service of emigrants traveling West and the U.S. military.

The Louisiana Purchase of 1803 has been called the greatest bargain in American history. The treaty of cession with France gave the U.S. a vast tract of 828,000 square miles at a cost of less than five cents an acre and, in advancing the nation’s western boundary from the Mississippi to the Rocky Mountains, more than doubled its territory. Neither Napoleon nor the American negotiators knew just what had been bought: the Louisiana Purchase was at this point unexplored, its boundaries confused. Less than one percent of it was settled by whites; the rest was in the possession of Native Americans. Much of the new acquisition consisted of the Great Plains, a grassy, treeless, largely arid expanse. Extending all the way from Canada to Texas, it was drained by one of the world’s great river systems — the Mississippi and its tributaries. Although in 1800 the tide of white settlement had been flowing westward for two centuries, it had reached the Mississippi only a few places. Now, however, a new West had been acquired to fire the imagination and challenge the enterprise of a restless, growing nation.