Lewis and Clark's main accomplishments were mapping out a large portion of North America, establishing trade with Native Americans and contributing to the biological knowledge of the country, specifically the Pacific Northwest. However, they also definitively proved that a Northwest Passage did not exist.
Though Lewis and Clark opened the way for trade with Native Americans, they also paved the way for the changes to their way of life that followed, according to Nebraska Studies.
The Northwest Passage was a hoped-for waterway from the Missouri River to the Pacific Ocean to connect trade routes. Although Lewis and Clark established that such a route did not exist, they also made it clear that the area could be traveled by land.