St. Louis shaped the West. President Thomas Jefferson knew that the Spanish and British had mapped much of the Pacific Coast and Canada. The Lewis and Clark Expedition was part of Jefferson’s vision for the United States and the ongoing struggle among nations for supremacy in North America. In 1803, Jefferson asked Meriwether Lewis to lead this critical mission. In May 1804, Lewis, Clark, and a crew of about 50 set out from the St. Louis area. They returned to St. Louis in September 1806. More would go west from St. Louis to trade and explore, shaping the future of the continent.