confirmed that the Assiniboine held a vast territory across the northern plains, including into the United States (which achieved independence in 1776 but did not acquire the plains until 1803 in the Louisiana Purchase from France.) The Assiniboine became reliable and important trading partners and middlemen for fur traders and other Indians, particularly the British Hudson's Bay Company and North West Company, operating in western Canada in a vast area known then as Rupert's Land. During the later 18th century and early 19th century, south of the border in what became Montana and the Dakota territories, the Assiniboine traded with the American Fur Company and the competing Rocky Mountain Fur Company. The Assiniboine obtained guns, ammunition, metal tomahawks, metal pots, wool blankets, wool coats, wool leggings, and glass beads, as well as other goods from the fur traders in exchange for furs. Beaver furs and bison hides were the most commonly traded furs. Increased contact with Europeans resulted in Native Americans contracting Eurasian infectious diseases that were endemic among the Europeans. They suffered epidemics with high mortality, most notably smallpox among the Assiniboine. The Assiniboine population crashed from around 10,000 people in the late 18th century to around 2600 by 1890. The Lewis and Clark Expedition was mounted by the United States in 1804–1806 to explore the Louisiana Territory, newly acquired from France. The expedition's journals mention the Assiniboine, whom the party heard about while returning from Fort Clatsop down the Missouri River. These explorers did not encounter or come in direct contact with the tribe. Noted European and American painters traveled with traders, explorers, and expeditions for the opportunity to paint the West and its Native American peoples. Among those who encountered and painted the Assiniboine from life were painters Karl Bodmer, Paul Kane, and George Catlin. The Assiniboine signed the Treaty of Fort Laramie (1851). In 1885, some Assiniboine scouts aided the Canadian North West Field Force track down Cree renegades who were participating in the Second Riel Rebellion of Métis. Interactions with other tribes In 1857, a group of Sioux warriors, including Sitting Bull, attacked an Assiniboine camp, they had killed all except an 11-year-old boy who was still fighting against the raiders with his child-sized bow. Some Sioux warriors threatened to kill him, but before they could, he turned to Sitting Bull and wrapped his arms around his waist and said "please brother don't kill me!"