The famous expedition that explored the American West in the early 19th century is the Lewis and Clark Expedition. Commissioned by President Thomas Jefferson in 1804, the journey aimed to explore the newly acquired Louisiana Territory, map the region, and find a water route to the Pacific Ocean. Led by Meriwether Lewis and William Clark, the expedition covered thousands of miles, providing invaluable information about the geography, natural resources, and Native American tribes encountered along the way. Their findings significantly contributed to westward expansion and increased the understanding of the vast territories of the United States.