Events leading to the Battle of the Washita began with the Sand Creek Massacre of 1864. On November 29, troops under the command of Colonel J.M. Chivington attacked and destroyed the Cheyenne camp of Chief Black Kettle and Chief White Antelope on Sand Creek, 40 miles from Fort Lyon, Colorado Territory. Black Kettle's band flew an American flag and a white flag, and considered themselves at peace and under military protection. The terrible slaughter caused a massive public outcry. In response, a federal Peace Commission was created to convert Plains Indians from their nomadic way of life and settle them on reservations.

On the Southern Plains, the work of the Commission culminated in the Medicine Lodge Treaty of October 1867. Under treaty terms the Arapahos, Cheyennes, Comanches, Kiowas, and Plains Apaches were assigned to reservations in the Indian Territory. There they were supposed to receive permanent homes, farms, agricultural implements, and annuities of food, blankets, and clothing. The treaty was doomed to failure. Many tribal officials refused to sign. Some who did sign had no authority to compel their people to comply with such an agreement. War parties, mostly young men violently opposed to reservation life, continued to raid white settlements in Kansas.

Major General Philip H. Sheridan, in command of the Department of the Missouri, adopted a policy that "punishment must follow crime." In retaliation for the Kansas raids, he planned to mount a winter campaign when Indian horses would be weak and unfit for all but the most limited service. The Indians' only protection in winter was the isolation afforded by brutal weather.

Black Kettle and Arapaho Chief Big Mouth went to Fort Cobb in November 1868 to petition General William B. Hazen for peace and protection. A respected leader of the Southern Cheyenne, Black Kettle had signed the Little Arkansas Treaty in 1865 and the Medicine Lodge Treaty in 1867. Hazen told them that he could not allow them to bring their people to Fort Cobb for protection because only General Sheridan, his field commander, or Lieutenant Colonel George Custer, had that authority. Disappointed, the chiefs headed back to their people at the winter encampments on the Washita River.

Even as Black Kettle and Big Mouth parlayed with General Hazen, the 7th Cavalry established a forward base of operations at Camp Supply, Indian Territory as part of Sheridan's winter campaign strategy. Under orders from Sheridan, Custer marched south on November 23, 1868 with about 800 troopers, traveling through a foot of new snow. After four days travel the command reached the Washita valley shortly after midnight on November 27, and silently took up a position near an Indian encampment their scouts had discovered at a bend in the river.