In 1801, Thomas Jefferson became the third President of the United States. Jefferson feared that France, led by General Napoleon Bonaparte, was going to expand its empire in the Americas. New Orleans in Louisiana was an important trading port for American farmers on the Mississippi River so Jefferson decided to approach France about purchasing New Orleans.

When approached about the sale of New Orleans, the French government surprised the Americans by offering to sell the whole territory of Louisiana to the United States. The Louisiana Purchase in 1803 included land as far west as Idaho and north as Canada. To explore the new territory and find a route to the Pacific Ocean, Jefferson asked Meriwether Lewis and William Clark to head an expedition. Sacagawea, a Shoshone woman, joined the expedition as their translator.

The Corps of Discovery led by Lewis and Clark, set out on May 14, 1804. It consisted of soldiers, trappers, scouts, Native Americans, and an enslaved African American. After traveling 8,000 miles, the expedition reached the Pacific Ocean in November 1805.