Throughout his presidency at the beginning of the 19th century, Thomas Jefferson had worried about the future of the western U.S., seeing that settlements in the Ohio Valley and lower South relied upon the Mississippi River. France's controls over the region, in his estimation, put the U.S. at a severe disadvantage. His solution proved successful beyond his wildest imagination, for Napoleon did not only sell New Orleans to the U.S, the portion that Jefferson instructed his ministers to make an offer on, but all of "New France," the entire area of Louisiana. Jefferson might have said later that his purchase of the territory "strained" but did not "break" the Constitution, but also should have boasted that, with one stroke, he had removed one less obstacle to American expansionism.

The Louisiana Purchase encompassed all or part of 15 current U.S. states and two Canadian provinces, including Arkansas, Missouri, Iowa, Oklahoma, Kansas, Nebraska, parts of Minnesota that were west of the Mississippi River, most of North Dakota, nearly all of South Dakota, northeastern New Mexico, Northern Texas, the portions of Montana, Wyoming, and Colorado east of the Continental Divide, and Louisiana west of the Mississippi River, including the city of New Orleans (parts of this area were still claimed by Spain at the time of the Purchase.) In addition, the Louisiana Purchase contained small portions of land that would eventually become part of the Canadian provinces of Alberta and Saskatchewan. The purchase, which doubled the size of the young nation, comprises around 23% of current American territory.

The purchase allowed Jefferson to plan something he had talked about since taking office: an expedition deep into the unmapped and largely unknown continent with the final destination being the Pacific Ocean. This could prove the most significant of the goals that Jefferson - a person who thought of himself as a scientifically-minded thinker - wanted to accomplish as president.

Given that Lewis and Clark remain so famous, it was inevitable that the other American explorers would be overlooked, particularly William Eaton, the hero of the Battle of Derna in the Barnaby Wars, and Zebulon Montgomery Pike, the explorer of the Mississippi. In the case of Pike, Orsi suggests that the explorer is overlooked and in some cases slighted due to what the expeditions did and did not accomplish. Eaton and Pike represented "the first wave of Manifest Destiny, expanding the republican principles of liberty and citizenship in the world."

Contrasted to that patriotic sentiment are caveats and questions. The career of Zebulon Pike was "dominated by ambiguously motivated explorations of the American West."[2] With the procurement of the Louisiana Purchase, which doubled the size of the nation, Pike had the full force of American authority at his disposal, and his travels through the Colorado Rockies into New Mexico pushed the boundaries between America and Spain. Captured by Spanish officials for illegal entry, he was finally released back into American custody after a year's time with a volume of new information on Spanish territory, its economy, and its military configuration. This sparked a debate about whether the capture was planned by the American government itself.

Pike's return is still debated, as is his relationship with General James Wilkinson and Aaron Burr. The controversy is relevant to Burr's alleged conspiracy to establish a competing empire in the American Southwest, or perhaps as a way of conquering Spanish America without involving the White House. Pike's papers, confiscated by the Spanish, have complicated the search for the truth, and any evidence of his complicity remains confidential, in part because of the unpredictable explorer's unpredictable demise.