President Thomas Jefferson, James Monroe, and French Emperor, Napoleon Bonaparte, were involved with the purchase while the land was explored by mapping the territory, recording all plant and animal life, and engaging peacefully with Natives by Meriwether Lewis and William Clark dispatched to lead a band of soldiers.
”Napoleon offered the American negotiation minister, James Monroe, the whole of the Louisiana Territory, Jefferson happily accepted the deal. Jefferson directed Lewis and Clark to first and foremost find the elusive Northwest Passage, a body of water believed to connect the Mississippi River to the Pacific Ocean. Jefferson also instructed the explorers to record all the plant and animal life they encountered, map the territory, and engage with the Native peoples of the region on friendly terms” (“Expansion and Exploration New Republic”).
This direct quote tells you that Napoleon, the French Emperor, was the one who negotiated the territory with James Monroe, the negotiation minister for America, and sold the territory to Thomas Jefferson, the president of America at the time. Jefferson was pleased with the deal and dispatched Lewis and Clark on an expedition leading a band of soldiers so they could explore the land. They were instructed by Jefferson to map out the land, peacefully interact with the Natives on friendly terms, and record all life they encountered.
Map of Sac and Fox Lands along the Mississippi River from General William Clark, St. Louis, 11 September 1834, Digital Public Library of America
This image is a map of part of the territory of the Louisiana Purchase made by Louis and Clark. This shows that Louis and Clark explored the land because they made the map. This also shows how they explored it because this means they made maps of only parts of the territory so they could explore it easier.