Their ancestors had been woodland people farther east, and the full transition to equestrian plains culture had occurred over the course of the eighteenth century, as they acquired horses and moved westward.

By the mid-nineteenth century, the Oglala and Brulé bands of the Lakota were established powers in the Powder River region, and the combination of their military strength, their mobile equestrian culture, and their numbers made them arguably the most powerful Indigenous nation on the northern plains.

The Powder River Country was explicitly recognized as Lakota and allied peoples’ territory in the Fort Laramie Treaty of 1851, which established a framework of territorial boundaries between the various nations of the plains and the United States.

The treaty acknowledged Lakota claims to a vast area of the northern plains, including the Powder River region.