The Louisiana Purchase was actually a pretty shady deal. Jefferson bought it from the french without the approval of the people. His goal was that he wanted to expand the territory of the U.S. Previously the american people wouldn't go past the mountain range for fear of foreign colonies and native Americans. This purchase also ended up opening a trade route from coast to coast. While technically Lewis and Clarke went farther than they were supposed to, there was no one that could really contest them.
The film doesn't always improve the viewers understanding, the film could be lying that it's "based on real events". The film maker doesn't always know the real truth.
