Jefferson needed a party of men to explore, record, map and tell the nation about the new Louisiana Purchase land – and the land beyond that as well.
He needed a trained and disciplined group, and so he planned a military expedition.
He decided it should be led by his secretary, Meriwether Lewis, and Lewis's friend, William Clark. Under their command would be 32 other men – including four sergeants, 23 privates, and some non-military members, including Clark's slave York – and a Newfoundland dog named Seaman
