In the aftermath of the Dakota War of 1862, the U.S. government continued to punish the Sioux, including those who had not participated in the war. Large military expeditions into Dakota Territory in 1863 pushed most of the Sioux to the western side of the Missouri River and made safer the frontier of white settlement in Minnesota and the eastern Dakotas. An important impetus to another military campaign against the Sioux was the desire to protect lines of communication with recently discovered goldfields in
Montana and
Idaho. The lifeline for the American gold miners were
steamboats plying the
Missouri River through the heart of Sioux territory. During the winter of 1863–1864, Sully's superior,
Major General John Pope ordered Sully to establish several forts along the Missouri River and in the eastern Dakotas to secure the communication routes to the goldfields and to eliminate the Sioux threat to the settlers east of the Missouri River. Sully's army was the largest ever assembled to combat the
Plains Indians, comprising more than 4,000 men, many of them in support and supply roles along the
Missouri and
Yellowstone Rivers. Sully established
Fort Rice on the Missouri River in what is now North Dakota on July 7, 1864. From there, he led 2,200 men into western Dakota Territory. In the
Battle of Killdeer Mountain on July 28, Sully defeated about 1,600 Sioux warriors. After the battle the Sioux, along with their women and children, scattered into the
Badlands west of Killdeer Mountain, near where the present-day South Unit of
Theodore Roosevelt National Park is located. The Dakota badlands are characterized by "deep, impassable ravines" and "high rugged hills." Although running short of rations, Sully decided to continue his pursuit of the Sioux. A
Blackfoot scout said he knew a route through the Badlands passable by Sully's wagon train. After resting, Sully and his men plunged into the unknown terrain ahead. His objective was to continue to pursue the Sioux through the Badlands and then resupply his expedition by marching north to the
Yellowstone River where two steamboats full of rations awaited him. Sully followed the
Heart River upstream, entering the Badlands on August 5. "One minute they were rolling along on what seemed like limitless prairie; the next men and horses were lost in a maze of narrow gullies and malevolent steeps." Traveling with Sully was an emigrant wagon train of miners and their wives and children. Lakota leader
Sitting Bull described the Indians in the Battle of the Badlands as
Hunkpapas,
Sans Arcs, and
Miniconjou Lakota, Yanktonai, and others. ==The battle==