Background

When Jefferson became President in 1801 the Louisiana Purchase had not yet been made and the area around the headwaters of the Missouri and Columbia rivers was still unexplored by whites. This vast region was not part of the United States and its status was uncertain; it was said to belong to France or Spain or Great Britain, or to nobody.

One of the first measures of Jefferson's new administration was to provide for adequate examination of this region, believed to be rich in furs, timber, and minerals. In the winter of 1802–03 Congress agreed to an appropriation of $2,500 for the purpose. Jefferson organized the party as a military expedition sent out by the War Department.

Meriwether Lewis, Jefferson's private secretary, was put in command. Lewis asked that William Clark, an old friend and a fellow soldier, be made co-leader of the expedition. Lewis was given a captain's commission, and Clark was made a lieutenant. Lewis refused to recognize the difference in rank. Clark was addressed as “captain” from start to finish and is called “captain” to this day.

Lewis and Clark were men of exceptional physical and mental ability, and worked well together as a team. Both had long experience in wilderness living and river travel. Lewis was the natural leader and had the more scientific mind. Clark was a skilled frontiersman with a genius for negotiating with Indians.

Interesting facts about the Lewis and Clark expedition
For their leadership, Meriwether Lewis and William Clark each received 1,600 acres (650 hectares) of land as rewards. The rest of the men got double pay and 320 acres (130 hectares). The interpreter Toussaint Charbonneau received an additional $533.33 for his services. His wife Sacagawea got nothing.
The explorers passed through what are now 11 states: Illinois, Missouri, Iowa, Kansas, Nebraska, South Dakota, North Dakota, Montana, Idaho, Oregon, and Washington.
Sacagawea, the only woman to make the round trip, gave birth to a boy, Jean Baptiste, on Feb. 11, 1805. After the expedition, Charbonneau and Sacagawea asked Clark to raise and educate the boy, and he agreed.
Several members of the party often teamed up to communicate with the Indians. To talk to the Shoshone, for example, Lewis and Clark spoke in English to Private Francois Labiche. Labiche spoke in French to Toussaint Charbonneau. Charbonneau spoke in Hidatsa to Sacagawea, who spoke in Shoshone to members of her tribe.
York, the only black member of the expedition, had been a slave in the Clark family since boyhood. William Clark’s father, John Clark, gave William rights to York in his will.
Seaman, the only pet to accompany the explorers, was a Newfoundland dog owned by Lewis. Seaman proved to be especially dependable for guard duty. Indians once kidnapped Seaman, but the explorers rescued the dog.
The journals of Lewis and Clark describe about 180 plants and 125 animals that had not been reported to scientists.