The Lewis and Clark Expedition, also known as the Corps of Discovery Expedition, was the United States expedition to cross the newly acquired western portion of the country after the Louisiana Purchase. The Corps of Discovery was a select group of U.S. Army and civilian volunteers under the command of Captain Meriwether Lewis and his close friend Second Lieutenant William Clark. Clark and 30 members set out from Camp Dubois, Illinois, on May 14, 1804, met Lewis and ten other members of the group in St. Charles, Missouri, then went up the Missouri River. The expedition crossed the Continental Divide of the Americas near the Lemhi Pass, eventually coming to the Columbia River, and the Pacific Ocean in 1805. The return voyage began on March 23, 1806, at Fort Clatsop, Oregon, and ended on September 23 of the same year.

President Thomas Jefferson commissioned the expedition shortly after the Louisiana Purchase in 1803 to explore and to map the newly acquired territory, to find a practical route across the western half of the continent, and to establish an American presence in this territory before European powers attempted to establish claims in the region. The campaign's secondary objectives were scientific and economic: to study the area's plants, animal life, and geography, and to establish trade with local Native American tribes. The expedition returned to St. Louis to report its findings to Jefferson, with maps, sketches, and journals in hand.

The Lakota (pronounced [laˈkˣota]; Lakota: Lakȟóta/Lakhóta) are a Native American people. Also known as the Teton Sioux (from Thítȟuŋwaŋ), they are one of the three prominent subcultures of the Sioux people. Their current lands are in North and South Dakota. They speak Lakȟótiyapi—the Lakota language, the westernmost of three closely related languages that belong to the Siouan language family.

The seven bands or "sub-tribes" of the Lakota are:

Sičháŋǧu (Brulé, Burned Thighs)

Oglála ("They Scatter Their Own")

Itázipčho (Sans Arc, Without Bows)

Húŋkpapȟa (Hunkpapa, "End Village", Camps at the End of the Camp Circle)

Mnikȟówožu (Miniconjou, "Plant Near Water", Planters by the Water)

Sihásapa ("Blackfeet” or “Blackfoot")

Oóhenuŋpa (Two Kettles)Notable Lakota persons include Tȟatȟáŋka Íyotake (Sitting Bull) from the Húnkpapȟa, Maȟpíya Ičáȟtagya (Touch the Clouds) from the Miniconjou, Heȟáka Sápa (Black Elk) from the Oglála, Maȟpíya Lúta (Red Cloud) from the Oglála, Billy Mills from the Oglála, Tȟašúŋke Witkó (Crazy Horse) from the Oglála and Miniconjou, and Siŋté Glešká (Spotted Tail) from the Brulé. More recent activists include Russell Means from the Oglála.