Question

How did the United States strengthen its control over territory in North America in the early nineteenth century by making the Louisiana Purchase and subsequently financing the Lewis & Clark Expedition?

Answer 1

Though the territory of Louisiana had changed hands many times between France and Spain, Spain ceded the territory to France by Napoleon in 1800. Napoleon, whose focus in Europe was absorbed by war, started to see the region as a burden of needlessness. In 1803 he offered to sell all 828,000 square miles to the US for a $15 million bargain price.
Jefferson adhered to a strict reading of the Constitution and believed that purchasing the Louisiana Territory could be plausibly illegal without a clear enumeration of his right as President to obtain the purchase.

Jefferson authorized an expedition to the West led by US Army volunteers Captain Meriwether Lewis and Second Lieutenant William Clark to explore and map all of this new territory. Their expedition lasted from 1803 to 1806 and was greatly supported by Sacagawea, a Shoshone woman who acted as their guide. Without the tremendous knowledge of Sacagawea's land and the Indian tribes that occupied it, Lewis and Clark's expedition may easily have encountered disaster.

The Louisiana Purchase proved famous among white Americans, who were hungry to settle for more western lands. The deal helped Jefferson navigate a landslide to secure reelection in 1804. Of the 176 votes cast, all but 14 have been in his favour.
The Louisiana Purchase's great expansion of the United States attracted criticism, however, especially from northerners who feared the inclusion of more slave states and a resulting lack of representation of their interests in the North. New western lands would be a blessing for the southern slaveholders; the Louisiana Purchase sought to engrave and extend their misery to western territory for the enslaved people.