If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

The Louisiana Purchase and its exploration

In 1803, Jefferson made a controversial decision that effectively doubled the territory of the United States while transgressing his own views of proper presidential authority.


  • The Louisiana Purchase doubled the size of the United States, reshaping the environmental and economic makeup of the country.
  • Jefferson confronted questions of presidential authority in deciding whether or not to acquire the territory, since the US Constitution does not explicitly give the president the power to purchase territory.
  • Jefferson enlisted Meriwether Lewis and William Clark to explore the new uncharted territory and secured Congressional funding for their expedition.

The Louisiana Purchase

Though the Louisiana territory had changed hands between France and Spain a number of times, in 1800 Spain ceded the territory to Napoleon’s France. Napoleon, whose attention was consumed by war in Europe, began to view the territory as a needless burden. In 1803, he volunteered to sell all 828,000 square miles to the United States for the bargain price of $15 million.
Jefferson adhered to a strict interpretation of the Constitution and believed that without a specific enumeration of his right as president to acquire the purchase, buying the Louisiana Territory could plausibly be unconstitutional. The Federalists opposed the purchase for several reasons, chief among them the likelihood that new slave states would enter the Union from the southern parts of the territory.
Despite Federalist opposition and the contested constitutionality of the purchase, Jefferson agreed to the deal, which almost doubled US territory. He said to his Cabinet regarding the Purchase: “"it is the case of a guardian, investing the money of his ward in purchasing an important adjacent territory; & saying to him when of age, I did this for your good.” 1 Jefferson was correct to assume that the Louisiana Territory would be an important element to the United States’ future.
The area acquired by the Louisiana Purchase. Image courtesy of Wikimedia Commons.

Lewis and Clark's expedition

In order to explore and map all of this new territory, Jefferson authorized a westward expedition led by US Army volunteers Captain Meriwether Lewis and Second Lieutenant William Clark. Their expedition lasted from 1803 to 1806 and was aided tremendously by the help of a Shoshone woman, Sacagawea, who served as their guide. Without Sacagawea’s immense knowledge of the land and the Indian tribes that inhabited it, Lewis and Clark’s expedition could easily have met with disaster.
Detail from mural of Sacagawea guiding Lewis and Clark. Mural by Edgar Samuel Paxson, c. 1912, on view at the Montana State Capitol. Image courtesy of Wikimedia Commons.
The Louisiana Purchase proved popular with white Americans, who were hungry for more western lands to settle. The deal helped Jefferson win reelection in 1804 by a landslide. Of 176 electoral votes cast, all but 14 were in his favor.
The great expansion of the United States achieved by the Louisiana Purchase did receive criticism, though, especially from northerners who feared the addition of more slave states and a corresponding lack of representation of their interests in the North. For southern slaveholders, new western lands would be a boon; for enslaved people, the Louisiana Purchase threatened to entrench and expand their suffering to western territories.

Environmental impacts

Lewis and Clark made meticulous notes of any flora and fauna they encountered during their journey. Enormous clouds of gnats and mosquitos swarmed about their heads as they made their way up the Missouri River. They encountered (and killed) a variety of animals including elk, buffalo, and grizzly bears. One member of the expedition survived a rattlesnake bite. As the men collected minerals and specimens of plants and animals, the overly-curious Lewis sampled minerals by tasting them and became seriously ill at one point.
They sketched and documented over 260 plants in their journals, a majority of them new to scientific discovery. They also made the first scientific discoveries of many bird species, reptiles, and mammals. Yet as new settlers came to make their lives on the western frontier, preserving these newfound species was hardly their concern. 2

What do you think?

Why did many Federalists question the constitutionality of the Louisiana Purchase?
Make a list of the benefits and drawbacks of the Louisiana Purchase. If you were President Jefferson, would you have decided to acquire the territory?
How did the Louisiana Purchase align with Jefferson’s vision of an agrarian America?

Want to join the conversation?