The Treaty of Fort Laramie (1868) granted the Lakota Sioux and their northern Cheyenne allies a reservation, including the Black Hills, in Dakota Territory and a large area of "unceded territory" in what became Montana and Wyoming.
Both areas were for the exclusive use of the Indians, and whites, except for government officials, were forbidden to trespass.
In 1874, the discovery of gold in the Black Hills caused the United States to attempt to buy the Black Hills from the Sioux.
 The U.S. ordered all bands of Lakota and Cheyenne to come to the Indian agencies on the reservation by January 31, 1876 to negotiate the sale.
Some of the bands did not comply and when the deadline of January 31 passed, the Commissioner of Indian Affairs, John Q. Smith, wrote that "without the receipt of any news of Sitting Bull's submission, I see no reason why... military operations against him should not commence at once."
On February 8, 1876, General Phillip Sheridan telegraphed Generals George R. Crook and Alfred Howe Terry, ordering them to undertake winter campaigns against the "hostiles".

In bitterly cold weather, Brigadier General George Crook, commander of the Department of the Platte, marched north with the Big Horn Expedition from Fort Fetterman near present-day Douglas, Wyoming, on March 1.
General Crook's objective was to strike against the Indians while they were at their most vulnerable in winter camps.
Sitting Bull, Crazy Horse, and their followers were thought to be on the Powder, Tongue, or Rosebud rivers.
Crook's force consisted of 883 men, including United States Cavalry and Infantry, civilian packers, scouts, guides, and a newspaper reporter.
 Crook's highly valued chief scout was Frank Grouard, who had lived among the Lakota and spoke their language.

The soldiers had to heat their forks in the coals of their fires to prevent the tines from freezing to their tongues.
A blizzard on March 5 deposited over a foot of snow and significantly delayed Crook's progress.
Temperatures fell so low that the thermometers of the day could not record the cold.
Crook's column slowly followed the Bozeman Trail north to Old Fort Reno, reaching it on March 5.
There, the expedition established its supply base, leaving the wagons and Infantry accompanying the column, Companies C, and I, of the 4th U.S. Infantry, under Captain Edwin M. Coates.
The five Cavalry battalions then marched to the head of Otter Creek.
On March 16, scout Frank Grouard saw two Indian warriors observing the soldiers.
He identified them as Oglala Lakota and believed that the camp of Crazy Horse might be nearby.
This was reported to Crook, and at 5 p.m. he divided his command and sent Colonel Joseph J. Reynolds (a West Point classmate of President Ulysses S. Grant, and a combat veteran of both the Mexican–American War, and Civil War) on a night march with about 383 men, with rations for one day, following the trail of the two Oglalas southeast toward Powder River.
Crook kept with him about 300 men.
That night Frank Grouard and the other scouts followed the two Oglala Sioux's trail in the snow.
It led right to what they were looking for, an Indian village, which they described as containing more than 100 lodges on the west bank of Powder River.
The scouts immediately reported this information back to Colonel Reynolds.
The Treaty of Fort Laramie (1868) granted the Lakota Sioux and their northern Cheyenne allies a reservation, including the Black Hills, in Dakota Territory and a large area of "unceded territory" in what became Montana and Wyoming. Both areas were for the exclusive use of the Indians, and whites, except for government officials, were forbidden to trespass. In 1874, the discovery of gold in the Black Hills caused the United States to attempt to buy the Black Hills from the Sioux.  The U.S. ordered all bands of Lakota and Cheyenne to come to the Indian agencies on the reservation by January 31, 1876 to negotiate the sale. Some of the bands did not comply and when the deadline of January 31 passed, the Commissioner of Indian Affairs, John Q. Smith, wrote that "without the receipt of any news of Sitting Bull's submission, I see no reason why... military operations against him should not commence at once." On February 8, 1876, General Phillip Sheridan telegraphed Generals George R. Crook and Alfred Howe Terry, ordering them to undertake winter campaigns against the "hostiles".
In bitterly cold weather, Brigadier General George Crook, commander of the Department of the Platte, marched north with the Big Horn Expedition from Fort Fetterman near present-day Douglas, Wyoming, on March 1. General Crook's objective was to strike against the Indians while they were at their most vulnerable in winter camps. Sitting Bull, Crazy Horse, and their followers were thought to be on the Powder, Tongue, or Rosebud rivers. Crook's force consisted of 883 men, including United States Cavalry and Infantry, civilian packers, scouts, guides, and a newspaper reporter.  Crook's highly valued chief scout was Frank Grouard, who had lived among the Lakota and spoke their language.
The soldiers had to heat their forks in the coals of their fires to prevent the tines from freezing to their tongues. A blizzard on March 5 deposited over a foot of snow and significantly delayed Crook's progress. Temperatures fell so low that the thermometers of the day could not record the cold. Crook's column slowly followed the Bozeman Trail north to Old Fort Reno, reaching it on March 5. There, the expedition established its supply base, leaving the wagons and Infantry accompanying the column, Companies C, and I, of the 4th U.S. Infantry, under Captain Edwin M. Coates. The five Cavalry battalions then marched to the head of Otter Creek. On March 16, scout Frank Grouard saw two Indian warriors observing the soldiers. He identified them as Oglala Lakota and believed that the camp of Crazy Horse might be nearby. This was reported to Crook, and at 5 p.m. he divided his command and sent Colonel Joseph J. Reynolds (a West Point classmate of President Ulysses S. Grant, and a combat veteran of both the Mexican–American War, and Civil War) on a night march with about 383 men, with rations for one day, following the trail of the two Oglalas southeast toward Powder River. Crook kept with him about 300 men. That night Frank Grouard and the other scouts followed the two Oglala Sioux's trail in the snow. It led right to what they were looking for, an Indian village, which they described as containing more than 100 lodges on the west bank of Powder River. The scouts immediately reported this information back to Colonel Reynolds.
Battle of Powder River