Lewis and Clark Expedition

The Lewis and Clark Expedition, also called the Corps of Discovery, was a U.S. Army-led journey from the Mississippi River to the Pacific Ocean and back. It set out in 1804 and returned in 1806. Commissioned by President Thomas Jefferson, it gave the young nation its first detailed knowledge of much of the western interior, and it strengthened American claims to a vast region that was already home to many Native nations.

The background lay in Jefferson's long interest in the West and in the Louisiana Purchase of 1803, in which the United States acquired France's claim to a huge territory west of the Mississippi. Jefferson wanted the land explored for scientific, commercial, and political reasons. He hoped to find a practical water route across the continent, the long-imagined Northwest Passage, and to learn about the region's geography, plants, animals, and peoples. He chose his secretary, Meriwether Lewis, to lead the effort, and Lewis invited William Clark, an experienced frontier soldier, to share command.

The party left the St. Louis area in the spring of 1804 and traveled up the Missouri River by keelboat and smaller craft. They spent the winter of 1804–05 near Mandan and Hidatsa villages in present-day North Dakota. There they met the French-Canadian trader Toussaint Charbonneau and his young Shoshone wife, Sacagawea, who joined the expedition with her infant son. In 1805 the group crossed the Rocky Mountains with crucial help from the Shoshone, who supplied horses and guidance, then descended the Columbia River to the Pacific, reaching the coast late that year. They wintered near the river's mouth and returned east in 1806, reaching St. Louis in September.

The expedition did not find an easy all-water route, since the mountains made one impossible. But it produced journals, maps, and descriptions of dozens of previously undocumented plant and animal species. It also established contact, sometimes tense but largely peaceful, with many Native nations. Only one member of the party died on the journey, apparently of illness.

The legacy is complicated. The expedition inspired fur traders, settlers, and later government surveys, and it became a cornerstone of the American story of westward expansion. For Native peoples, however, it marked the start of growing pressure on their lands and ways of life. Modern accounts increasingly emphasize the Indigenous knowledge that made the journey possible, along with the contributions of Sacagawea and of York, the enslaved man who traveled with Clark. Together, these perspectives show an expedition that mapped a continent while also foreshadowing profound change.