The purpose of the Lewis and Clark Expedition in the early 1800s was to explore and map the newly acquired western territories of the United States following the Louisiana Purchase in 1803. Commissioned by President Thomas Jefferson, the expedition aimed to study the geography, natural resources, and inhabitants of the vast region stretching from St. Louis to the Pacific Ocean. Led by Meriwether Lewis and William Clark, the journey, which lasted from 1804 to 1806, involved mapping rivers, mountains, and various terrains, as well as establishing trade relations with Native American tribes. The expedition significantly contributed to the westward expansion of the United States and provided valuable scientific and geographic knowledge.