Final answer:
The accomplishment of the Lewis and Clark expedition was paving the way for American exploration and settlement in the western territories, establishing relationships with Native American tribes, collecting plant and animal specimens, and accurately mapping the territory.
Step-by-step explanation:
The accomplishment of the Lewis and Clark expedition was that it paved the way for future American exploration and settlement in the western territories of the United States. The expedition successfully established relationships with Native American tribes, collected plant and animal specimens, and accurately mapped the territory. Their achievements helped solidify U.S. claims to the vast western region.