Lewis and Clark led the first U.S. expedition to the Pacific Coast between 1804-1806 to map the newly acquired Louisiana Purchase territory, establish diplomatic relations with indigenous tribes, and study the region's natural resources and potential for economic use. Accompanied by Sacagawea as their guide, they mapped important new areas, made contact with dozens of Native American tribes, and established the U.S. claim to the western lands while commissioning by President Thomas Jefferson to explore the vast new territory and seek a water route to the Pacific.