When the United States purchased Louisiana for $15 million dollars in 1803, we gained 828,000 square miles of land and doubled the size of the United States, and along with it, many border disputes between the US, Britian, and Spain. The first conflict to arise was the border disputes between the Missouri Territory and Britian. The Convention of 1818 set the boundary at the 49th parallel. This gave the top of the Louisiana purchase, north of Montana, to the British. The next conflict that arose was a boundary dispute between Spain and the US. This lead to the Adams-Onís Treaty in which the US gained Florida and defined the US and the New Spain (now Mexico) border. Another conflict that occurred between the US and the British North American Colonies was the border disputes between Northeastern Minnesota and the British North American Colonies. The Webster-Ashburton Treaty resolved this issue by establishing the border between Lake Superior and Lake of the Woods and reaffirmed the border location at the 49th parallel and gave Maine to the US.
This article describes the Journey the Lewis and Clark and 42 other men took in 1803 through the new Louisiana land they had purchased from the French. It took many years for the US and France to settle all the border issues.
Some long range significance of the border disputes is that the border between Canada and the US today is still at the 49th parallel.