Humanities › History & Culture Why Did the Lewis and Clark Expedition Cross North America? The Epic Voyage to the Pacific Had an Official Reason and Real Reasons Share Flipboard Email Print Fotosearch / Archive Photos / Getty Images History & Culture American History Basics Important Historical Figures Key Events U.S. Presidents Native American History American Revolution America Moves Westward The Gilded Age Crimes & Disasters The Most Important Inventions of the Industrial Revolution African American History African History Ancient History and Culture Asian History European History Genealogy Inventions Latin American History Medieval & Renaissance History Military History The 20th Century Women's History View More By Robert McNamara History Expert Robert J. McNamara is a history expert and former magazine journalist. He was Amazon.com's first-ever history editor and has bylines in New York, the Chicago Tribune, and other national outlets. our editorial process Robert McNamara Updated January 24, 2020 Meriwether Lewis and William Clark and the Corps of Discovery crossed the North American continent from 1804 to 1806, traveling from St. Louis, Missouri to the Pacific Ocean and back. The explorers kept journals and drew maps during their voyage, and their observations greatly increased the available information about the North American continent. Before they crossed the continent there were theories about what lay in the West, and most of them made little sense. Even the president at the time, Thomas Jefferson, was inclined to believe some fanciful legends about the mysterious regions no white Americans had seen. The journey of the Corps of Discovery was a carefully planned venture of the United States government, and it was not conducted simply for adventure. So why did Lewis and Clark make their epic journey? In the political atmosphere of 1804, President Thomas Jefferson offered a practical reason that ensured Congress would appropriate funds for the expedition. But Jefferson also had several other reasons, ranging from purely scientific to a desire to thwart European nations from colonizing the western frontier of America. Earliest Idea for an Expedition Thomas Jefferson, the man who conceived of the expedition, was first interested in having men cross the North American continent as early as 1792, nearly a decade before he became president. He urged the American Philosophical Society, based in Philadelphia, to finance an expedition to explore the vast spaces of the West. But the plan did not materialize. In the summer of 1802, Jefferson, who had been president for a year, received a copy of a fascinating book written by Alexander MacKenzie, a Scottish explorer who had traveled across Canada to the Pacific Ocean and back. At his home at Monticello, Jefferson read MacKenzie's account of his travels, sharing the book with his personal secretary, a young army veteran named Meriwether Lewis. The two men apparently took the voyage of MacKenzie as something of a challenge. Jefferson resolved that an American expedition should also explore the Northwest. The Official Reason: Commerce and Trade Jefferson believed that an expedition to the Pacific could only be properly funded and sponsored by the US government. To obtain the funds from Congress, Jefferson had to present a practical reason for sending explorers into the wilderness. It was also important to establish that the expedition was not setting out to provoke war with the Indian tribes found in the western wilderness. And it was also not setting out to claim territory. Trapping animals for their furs was a lucrative business at the time, and Americans such as John Jacob Astor were building great fortunes based on the fur trade. And Jefferson knew that the British held a virtual monopoly on the fur trade in the Northwest. And as Jefferson felt that the US Constitution gave him the power to promote trade, he asked for an appropriation from Congress on those grounds. The proposal was that men exploring the Northwest would be seeking out opportunities where Americans could trap for furs or trade with friendly Indians. Jefferson requested an appropriation of $2,500 from Congress. There was some skepticism expressed in Congress, but the money was provided. The Expedition Was Also for Science Jefferson appointed Meriwether Lewis, his personal secretary, to command the expedition. At Monticello, Jefferson had been teaching Lewis what he could about science. Jefferson also sent Lewis to Philadelphia for tutoring from scientific friends of Jefferson's, including Dr. Benjamin Rush. While in Philadelphia, Lewis received tutoring in several other subjects Jefferson thought would be useful. A noted surveyor, Andrew Ellicott, taught Lewis to take measurements with a sextant and octant. Lewis would use the navigational instruments to plot and record his geographic positions while on the journey. Lewis also received some tutoring in identifying plants, as one of the duties assigned to him by Jefferson would be to record the trees and plants growing in the west. Likewise, Lewis was taught some zoology to help him accurately describe and classify any previously unknown animal species which were rumored to roam the great plains and mountains of the west. The Issue of Conquest Lewis picked his former colleague in the US Army, William Clark, to help command the expedition because of Clark's known reputation as an Indian fighter. Yet Lewis had also been cautioned not to engage in combat with Indians, but to withdraw if violently challenged. Careful thought was given to the size of the expedition. Originally it was thought that a small group of men would have a better chance of success, but they might be too vulnerable to potentially hostile Indians. It was feared a larger group might be seen as provocative. The Corps of Discovery, as the men of the expedition would eventually be known, ultimately consisted of 27 volunteers recruited from US Army outposts along the Ohio River. Friendly engagement with Indians was a high priority of the expedition. Money was allocated for "Indian gifts," which were medals and useful items such as cooking implements that could be given to Indians the men would meet on the way west. Lewis and Clark mostly avoided conflicts with Indians. And a Native American woman, Sacagawea, traveled with the expedition as an interpreter. While the expedition was never intended to start settlements in any of the areas traversed, Jefferson was well aware that ships from other nations, including Britain and Russia, had already landed in the Pacific Northwest. It's probable that Jefferson and other Americans at the time may have feared that other nations would begin settling the Pacific coast just as the English, the Dutch, and the Spanish had settled the Atlantic coast of North America. So one unstated purpose of the expedition was to survey the area and thus provide knowledge that could be useful to later Americans who would travel west. The Exploration of the Louisiana Purchase It is often said that the purpose of the Lewis and Clark Expedition was to explore the Louisiana Purchase, the vast land purchase that doubled the size of the United States. In fact, the expedition had been planned and Jefferson was intent on it proceeding before the United States had any expectation of purchasing land from France. Jefferson and Meriwether Lewis had been actively planning for the expedition in 1802 and early 1803, and the word that Napoleon wished to sell France's holdings in North American did not reach the United States until July 1803. Jefferson wrote at the time that the planned expedition would now be even more useful, as it would provide a survey of some of the new area now belonging to the United States. But the expedition was not originally conceived as a way to survey the Louisiana Purchase. Results of the Expedition The Lewis and Clark Expedition was considered a great success, and it did meet its official purpose, as it helped foster an American fur trade. And it also met the other various goals, especially by increasing scientific knowledge and providing more reliable maps. And the Lewis and Clark Expedition also strengthened a United States claim to the Oregon Territory, so the expedition did ultimately lead toward the settlement of the west.