Why was the expedition of captain meriwether lewis and lieutenant william clark, from 1804-1806, so important to the u.s.?

I believe the expedition was important because it opened up the west for the former colonists. Before Lewis and Clark, the people (besides the Native Americans) had pretty much no idea what was to the west of them. Lewis and Clark changed that by exploring and mapping a lot of what is now the western United States. 
Hope this helps! Please let me know if I'm wrong :)

se mas especifico hay muchas crisis en ese siglo