Final answer:
President Jefferson sent Lewis and Clark into the Louisiana Territory to improve American merchants' access to China, legitimize American claims to the land, establish trade with western tribes, and gather scientific information.
Step-by-step explanation:
President Jefferson sent Lewis and Clark into the Louisiana Territory for multiple reasons. Firstly, he wanted to establish a river route from St. Louis to the Pacific Ocean to improve American merchants' access to the ports of China and capture a portion of the profitable fur trade that had benefited Great Britain. Secondly, Jefferson aimed to legitimize American claims to the land against rivals like Great Britain and Spain. Lewis and Clark were instructed to map the territory they passed through and explore all tributaries of the Missouri River. Additionally, Jefferson wanted to pave the way for American trade among western tribes. Lastly, he had a keen interest in science and nature, so he ordered Lewis and Clark to take extensive notes on the geography, plant life, animals, and natural resources of the region they would journey through.