The largest division of a Native American group of seven related tribes, commonly known as the Sioux, who inhabit areas of Nebraska, Montana, the woodlands of Minnesota, and the eastern Dakotas on the fringe of the northern Great Plains. During the mid-18th century they lost much of their lands to the Ojibwa. As French and English fur trade increased, so did intertribal warfare, exterminating some tribes and driving others, including the Dakota, on to the plains. They raided the tribes of the Missouri River to the south-east, and also acted as middlemen, exchanging European goods, especially firearms, for corn, tobacco, and other produce. Traditional enemies and trade rivals were the Cree and Ojibwa to the north and east. In common with other Plains Peoples, the Dakota were nomadic buffalo hunters, who gathered in tribes during the summer, and dispersed into family groups during the winter. Before they acquired horses, buffalo hunting had been ecologically balanced; seasonal migrations were aided by the travois (sledge), pulled by dogs but later adapted for horses, and the tipi (Dakota for “they dwell”). Over-hunting with horses began to deplete the herds, further exacerbated by White people moving on to tribal lands and systematically devastating the herds.