Just two days later, the Expedition returned to the Hidatsa and Mandan villages, receiving warm greetings and good food.  The captains were sad to see that most of Fort Mandan had burned down, but they were even more disappointed to hear that their diplomacy had had so little impact on these tribes.  The Hidatsa had recently returned from a bloody raid on Cameawhait's Shoshoni band, while the Mandan and Arikara were preparing for war with one another. 

None of the Hidatsa chiefs were willing to risk a trip to see President Jefferson – even after Lewis and Clark gave one-eyed Chief Le Borgne a small swivel cannon to help defend his people. Others would also not be going downriver with the explorers.  John Colter joined two Illinois beaver trappers and headed back to the Yellowstone on 16 August, becoming one of the first and best-known "Mountain Men."  Charbonneau and Sacagawea also decided not to proceed on to St. Louis, preferring to stay with the Hidatsa.  The only new people joining the return voyage were the Mandan chief, Sheheke ("Big White") and his family, who agreed to go to Washington, D.C.

The most significant new development in Indian relations occurred on 21 August.  Arriving at an Arikara village, Lewis and Clark saw dozens of very large white tipis nearby and learned that the Cheyenne tribe was visiting.  The nomadic, buffalo-hunting Cheyenne were Algonquian speakers allied with the Arapaho.  Two centuries earlier, they had a Great Plains hunting and warring lifestyle on horseback. 

The Cheyenne had made an alliance with Hidatsa chief, Le Borgne, and wanted closer trade ties with the Arikara, as well.  These tribes had something in common – aggression by the Teton Lakota – and each had special products to exchange.  The Cheyenne needed vegetable crops that they no longer grew themselves and metal weapons that came through the Missouri River villages by way of British traders.  The farming Hidatsa and Arikara villagers desired the beautifully brain-tanned white buffalo hides and meat from Cheyenne hunters.

In meetings with Lewis and Clark, the Cheyenne chief displayed warm hospitality and great interest in an alliance with the United States. Grateful for his peace medal, the chief requested that American traders be sent to show his people how to trap and prepare for market the many beaver in his territory.  This small tribe of about 400 warriors, like the Shoshoni, Flathead, and Nez Perce, was desperate to obtain firearms from the United States to defend themselves from Sioux raiders.

In one of their final meetings with Indian leaders in the West, Lewis and Clark scored a diplomatic triumph with the friendly Cheyenne.  But they had to wonder why only the weakest tribes with little trade experience were the friendliest and most helpful, while the strongest Indian nations – l well-armed British allies with many furs to trade – disliked Americans with a passion. 

The experiences of Lewis and Clark showed that Indian tribes were unique and very different, but all had a sophisticated understanding of the major role that economics played in their lives.  It was harder to think of Indians as "wild and primitive savages" after the experiences of 1804-06.  But with the "best" tribes wanting trade only to get guns, it was also nearly impossible to believe in Jefferson's dream of a universal peace among all native nations.  The Louisiana Purchase unleashed powerful forces for change throughout the West and forever transformed the lives of all Indians.