How did Lewis and Clark's journey shape the US?

Initially tasked with exploring the Louisiana Purchase and scouting for a "northwest passage" to the Pacific Ocean, the US Army Captain Meriwether Lewis and Lieutenant William Clark led a "Corps of Discovery" west from St. Louis.  Lewis and Clark would travel just over 7,000 miles over the span of twenty-eight months.  Along the route, they lived off the land, relying on local guides and interpreters, including the legendary Sacajawea.  Trying to follow and float along rivers the Corps focused on trying to establish a navigable path to the then known Pacific Ocean.    
They departed St. Louis Missouri in May 14, 1804, reached the Pacific at the mouth of the Columbia River (Oregon) on November 15, 1805, and returned to St. Louis on September 23, 1806.  In all, 59 people volunteered for the expedition, with thirty-three reaching the Pacific, the balance staying at Fort Mandan, North Dakota.
Upon the successful completion of their mission, President Jefferson reported to congress that the expedition had been a great success, and consistent with the fiscally conservative nature of the times, launched into a lengthy explanation justifying the expense of the trip.  In all, Lewis and Clark made contact with roughly two dozen different Native American nations/tribes; mapped a route through the Dakotas, Montana, Idaho, and Oregon; and catalogued and gathered samples of hundreds of native plants, animals, and minerals. Perhaps most importantly, their travels mapped an early route for the Oregon Trail, which would lead to extensive western settlement over the next forty years.
Coupled with the Louisiana Purchase, Gadsden Purchase, and the Mexican American War Lewis and Clark’s expedition fully realized the manifest destiny of the young United States.  The mapping provided an understanding of the scope of the American Continent, establishing just how much land lay undeveloped.  What can be called European expansion came at the price of conquest and domination of Native American and Spanish/Mexican lands, which would become especially bitter as large numbers of European Americans pushed westward over the next century. 
National Park Service FAQ for Lewis and Clark Trail
 
High Res, zoom-able map of trail
https://www.nps.gov/lecl/faqs.htm