The U.S. mint prepared special silver medals with a portrait of Jefferson and had a message of friendship and peace, called Indian Peace Medals or peace medals. The soldiers were to distribute them to the nations they met. These symbolized U.S. sovereignty over the indigenous inhabitants. The expedition also prepared advanced weapons to display their military firepower. They also carried flags, gift bundles, medicine and other items they would need for their journey. Much time went into ensuring a sufficient supply of these items.
In 1803, President Thomas Jefferson commissioned the Corps of Discovery, and named U.S. Army Captain Meriwether Lewis its leader, who selected William Clark as his partner. Their goals were to explore the Louisiana Purchase, establish trade and U.S. sovereignty over the native peoples along the River Missouri. Jefferson also wanted to establish a U.S. claim of "Discovery" to the Pacific Northwest and Oregon territory by documenting an American presence there before Europeans could claim the land. According to some historians, Jefferson understood he would have a better claim of ownership to the Pacific Northwest if the team gathered scientific data on animals and plants.
Jefferson had a long interest in western expansion, and in 1780s met John Ledyard who discussed a proposed trip to the Pacific Northwest. When he became President, he asked Congress to fund expedition through the Louisiana Purchase, and to head to the Pacific Ocean. He used a secret message to Congress to ask them to fund the trip.
Thus Lewis and Clark had first to connect to lower Missouri to the Mandan country in North Dakota. Everything west from North Dakota to the Pacific was unknown, except that the Rocky Mountains existed and the upper Missouri seemed to flow from that direction. We might also mention methods of travel. Coronado and De Soto travelled with large gangs of armed men. Hearne and the younger Vérendrye joined bands of roving Indians. La Salle and Mackenzie used professional voyageurs and Indian guides. Lewis and Clark reached the Pacific mostly under their own power.
Before 1537 Cabeza de Vaca crossed central Texas or northern Mexico from the Gulf to northwest Mexico. In 1539-42 Hernando de Soto crossed much of the South from Georgia to Arkansas. In 1540-42 Francisco Vásquez de Coronado traveled from Arizona to eastern Kansas. Since these expeditions found nothing of value the Spaniards largely abandoned northward expansion. In 1608 the French founded Quebec and quickly spread through the Saint Lawrence basin. In 1682 René-Robert Cavelier, Sieur de La Salle went down the Mississippi from the Great Lakes to the Gulf. The French then established a chain of posts along the Mississippi from New Orleans to the Great Lakes. In 1714 Etiene Veniard, Sieur de Bourgmont ascended the Missouri as far as the mouth of the Cheyenne River in central South Dakota. In 1720 the Villasur expedition from Santa Fe was defeated by the Pawnee in eastern Nebraska. Pierre Gaultier de Varennes, sieur de La Vérendrye opened the area west of lake Superior and in 1738 reached the Mandan villages on the upper Missouri in North Dakota. In 1743 two of his sons reached, probably, the Big Horn Mountains of Wyoming. From Hudson Bay, in 1690 Henry Kelsey reached Saskatchewan River, in 1754 Anthony Henday followed the Saskatchewan almost to the Rocky Mountains and in 1771 Samuel Hearne reached the Arctic coast at the Coppermine River. In 1789 Sir Alexander Mackenzie (explorer) followed the river named after him to the Arctic Ocean. In 1793 he ascended the Peace River, crossed the Rocky Mountains and reached the Pacific twelve years before Lewis and Clark. Provoked by Russian expansion down the Alaska coast Juan José Pérez Hernández explored the Pacific coast in 1774 , followed by James Cook in 1778. This led to a British Sea Otter trade with China, the Nootka Crisis and Anglo-American claims on the Oregon country. In 1792 Robert Gray (sea captain) found the mouth of the Columbia River.
References to Lewis and Clark "scarcely appeared" in history books even during the United States centennial in 1876 and the expedition was largely forgotten despite having had a significant impact on increasing American owned land.
The Lewis and Clark Expedition (1804–1806) was the first United States expedition to the Pacific Coast. Commissioned by President Thomas Jefferson and led by two Virginia-born veterans of Indian wars in the Ohio Valley, Meriwether Lewis and William Clark, the expedition had several goals. Their objects were both scientific and commercial - to study the area's plants, animal life, and geography, and to discover how the region could be exploited economically. According to Jefferson himself, one goal was to find a "direct & practicable water communication across this continent, for the purposes of commerce with Asia" (the Northwest Passage). Jefferson also placed special importance on declaring U.S. sovereignty over the Native American tribes along the Missouri River, and getting an accurate sense of the resources in the recently-completed Louisiana Purchase. They were accompanied by a fifteen year old Shoshone Indian woman, Sacagawea, the wife of a French-Canadian fur trader. After crossing the Rocky Mountains, the expedition reached the Pacific Ocean in the area of present-day Oregon (which lay beyond the nation's new boundaries) in November 1805. They returned in 1806, bringing with them an immense amount of information about the region as well as numerous plant and animal specimens. Reports about geography, plant and animal life, and Indian cultures filled their daily journals. Although Lewis and Clark failed to find a commercial route to Asia, they demonstrated the possibility of overland travel to the Pacific coast. They found Native Americans in the trans-Mississippi West accustomed to dealing with European traders and already connected to global markets. The success of their journey helped to strengthen the idea that United States territory was destined to reach all the way to the Pacific. Although the expedition did make notable achievements in science, scientific research itself was not the main goal behind the mission.