Lewis & Clark: Jefferson's Mandate to Explore the Louisiana Purchase

President Thomas Jefferson commissioned the Corps of Discovery (1804–1806) led by Meriwether Lewis and William Clark with three interlocking objectives:

1. Explore the Louisiana Purchase (1803)

• 828,000 sq mi acquired from France for $15M — doubled U.S. size.
• Jefferson needed to know: geography, resources, rivers, mountains, flora, fauna, climate, native nations.
• No accurate maps existed beyond the Mississippi.

2. Find a Practical Route to the Pacific

• Seek a waterway or portage network (the hoped-for "Northwest Passage") connecting the Missouri/Columbia systems to the Pacific Ocean.
• Commercial imperative: U.S. claim to Oregon Country (vs. Britain) rested on discovery, occupation, and trade access.
• Result: They reached the Pacific via Columbia River (Nov 1805) but found no all-water route — the Rockies required difficult portages.

3. Establish Trade & Diplomatic Relations with Native Nations

• Meet every tribe encountered; distribute peace medals, flags, goods.
• Announce U.S. sovereignty; invite delegations to Washington.
• Assess tribal economies, territories, alliances, and willingness to trade furs/horses.
• Key partners: Mandan/Hidatsa (winter 1804–05), Shoshone (Sacagawea's people, horses for Rockies crossing), Nez Perce (rescue on return).

Bonus Objectives (Jefferson's Scientific Curiosity)

• Collect specimens (plants, animals, minerals) for American Philosophical Society.
• Record weather, latitude/longitude, languages, customs.
• Search for mastodons, salt mountains, Welsh-speaking Indians (myths of the era).

Outcome

• Route mapped: 4,000+ miles traversed; 140+ maps produced.
• Science: 178 new plants, 122 new animals described.
• Diplomacy: Relations opened with dozens of tribes.
• Sovereignty: U.S. claim to Pacific Northwest strengthened.
• No Northwest Passage: But proved overland transit possible.

The expedition was Jefferson's Enlightenment project—empirical inventory of an empire he bought sight unseen.