President Jefferson said that the United States was "miserably weak" compared to the large and powerful "great nation" of the Sioux in that portion of the Louisiana Purchase Territory.

On Sunday, 23 September, the Expedition dropped anchor at the site of present-day Pierre, South Dakota because 800-1,000 Teton Sioux of the Brule band were camped nearby in 140 tepees!  The Corps of Discovery had never seen such a large tribe with so many warriors who had been nearly unbeatable in battle.  Despite some fears, Lewis and Clark had to have a parley with the Teton to see if they were dangerous "river pirates" as many claimed or whether they would be America's helpful allies in the West. 

In their first meeting on Tuesday, 25 September, a large, well-armed Brule Teton delegation led by chiefs Black Buffalo, Partisan, and Buffalo Medicine arrived at the Americans' camp.  Things did not go well.  After drinking some whiskey, Chief Partisan and his men tried to capture one of the Expedition's pirogues (smaller boats), which was loaded with presents.  When he bumped against Clark and threatened him, the captain drew his sword.  Corpsmen grabbed their rifles, while the Indians loaded arrows into their bows, and everyone expected a bloody battle.

"Their treatment of me was very rough, and I think justified roughness on my part," Captain Clark would later write.  After a tense few moments of warriors and soldiers shouting insults to each other, Chief Black Buffalo stepped in and ordered his men to back off.  The two groups parted company without any violence but also without shaking hands.  That day, Clark recalled, left the Americans "in a bad humor" or mood.

The Americans and the Sioux almost came to blows over the boats later in the week.  But for most of two days in between, 26-27 September, Lewis and Clark enjoyed Teton hospitality in Black Buffalo's Brule camp.  When they arrived, the captains were hoisted high into the air on buffalo robes in a ceremony of respect for honored guests.  The Sioux feasted them at a grand barbecue of roast dog, 400 pounds of buffalo meat, and other special Indian dishes. 

Meetings were held in a large tepee, the council lodge, where 70 chiefs and elders sat in a circle of white, brain-tanned buffalo hides.  They smoked red stone calumets ("peace pipes") and delivered many speeches – most of which could not be understood by the Americans because their best interpreter, Dorion, was still downriver with the Yankton tribe.  Drumbeat dancing and singing went on for hours each evening, as the Indians entertained the explorers.

Although Lewis and Clark learned much about Teton Sioux ceremonies during these late September days, neither side liked or trusted the other.  Violence was possible at any time, mainly because both sides wanted to control the trade of the Missouri River.  The Americans needed Teton cooperation to change the region, but the Teton wanted the Americans to go away and leave things as they were.  The Sioux were so numerous, so powerful, and so well supplied with merchandise that they did not need trade with St. Louis or wish to be ruled by the U. S. president.

The Teton already obtained guns, metal kettles, cloth, and glass beads from other Sioux tribes in contact with British merchants in Canada.  The nomadic Teton hunters obtained all of the corn and other crops they needed from nearby farming Indians, such as the Arikara, Hidatsa, and Mandan. The Teton remained independent and free, able to purchase most European-made products or Indian-grown produce because their beautiful beaver pelts, heavy buffalo robes, and fast horses were in great demand by white merchants and other tribes, alike.  The ancient trading patterns along the Missouri River, which the Teton dominated, had given them a good life.  The cocky Americans from a new nation, which now claimed to own the key river of trade for the Teton, could only ruin their old and familiar good life.