The Fort Laramie Treaty of 1851 was signed on September 17, 1851, between United States treaty commissioners and representatives of the Cheyenne, Sioux, Arapaho, Crow, Assiniboine, Mandan, Hidatsa, and Arikara Nations. The treaty was an agreement between nine more or less independent parties. The treaty set forth traditional territorial claims of the tribes as among themselves. The United States acknowledged that all the land covered by the treaty was Indian territory and did not claim any part of it. The boundaries agreed to in the Fort Laramie treaty of 1851 would be used to settle a number of claims cases in the 20th century. The Native Americans guaranteed safe passage for settlers on the Oregon Trail and allowed roads and forts to be built in their territories in return for promises of an annuity in the amount of fifty thousand dollars for fifty years. The treaty should also "make an effective and lasting peace" among the eight tribes, each of them often at odds with a number of the others.
Although many European and European-American migrants to western North America had previously passed through the Great Plains on the Oregon and Santa Fe Trails, the California gold rush beginning in 1848 greatly increased traffic. The next year, both Thomas Fitzpatrick (agent of Upper Platte and Arkansas) and David D. Mitchell (superintendent at Saint Louis) recommended a council with the Indians to prevent a conflict. The United States government undertook negotiations with the Native American Plains tribes living between the Arkansas and Missouri rivers to ensure protected right-of-way for the migrants. The Congress had appropriated one hundred thousand dollars to the assembly, endorsed by Luke Lea (the Commissioner of Indian Affairs).
Because the area around Fort Laramie lacked forage for the Indians' horses, the treaty was negotiated and signed 30 miles downriver from the fort at the mouth of Horse Creek. Many Indians have referred to the treaty as the Horse Creek Treaty. Representatives from the Lakota, Cheyenne, Assiniboine, Gros Ventre, Mandan, Arikara, Hidatsa, Shoshone, Crow, and Arapaho took part in the treaty discussions.
The Comanche, Kiowa, and Kiowa Apache refused to send representatives to Fort Laramie because the fort was in Sioux territory. The Comanche, Kiowa, and Kiowa Apache considered the Sioux an enemy.
The United States Senate ratified the treaty, adding Article 5, to adjust compensation from fifty to ten years, if the tribes accepted the changes. Acceptance from all tribes, with the exception of the Crow, was procured. Several tribes never received the commodities promised as payments.
The Treaty Territories
The Lakota got some rather new territorial claims recognized. In 1823, a number of Lakotas had helped the United States army attack an Arikara village at Grand River (present South Dakota). The Lakotas had kept on pushing the village tribe north, so they got treaty on the former Arikara homeland along the Grand.
The Lakota received exclusive treaty rights to the Black Hills (present South Dakota), to the consternation of the Cheyenne and the Arapahoe. "... the Sioux were given rights to the Black Hills and other country that the Northern Cheyennes claimed. Their home country was the Black Hills, declared a Cheyenne historian in 1967. Arapahoe chief Black Coal complained in 1875: "I have never got anything yet for my land [the Black Hills]. It is part mine, and part the Sioux... In the first place, they came from the Missouri River and reached this place, and now they have got up this far, and they claim all this land."
The Cheyenne and Arapaho, the southernmost of the treaty tribes, held an area southward of the North Platte in common (mainly in present Wyoming and Colorado).
The Crow treaty territory (in present Montana and Wyoming) included the area westward from Powder River. Little Bighorn River ran through the center of the Crow domain.
After the Treaty
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The treaty was broken almost immediately after its inception, by the Lakota and Cheyenne attacking the Crow over the next two years.  In 1858, the failure of the United States to prevent the mass immigration of miners and settlers into Colorado during the Pike's Peak Gold Rush, also did not help matters. They took over Indian lands in order to mine them, "against the protests of the Indians," and founded towns, started farms, and improved roads. Before 1861, the Cheyenne and Arapahoe "had been driven from the mountain regions down upon the waters of the Arkansas." Such emigrants competed with the tribes for game and water, straining limited resources and resulting in conflicts with the emigrants. The U.S. government did not enforce the treaty to keep out the emigrants. In 1864 came the Sand Creek massacre on a camp of mostly Cheyennes by Colonel John M. Chivingtons army of one hundred days volunteers. The consequence was years of war between the Cheyennes and the United States.
The situation escalated with the Grattan affair in 1854, when a detachment of U.S. soldiers illegally entered a Sioux encampment to arrest those accused of stealing a cow, and in the process sparked a battle in which Chief Conquering Bear was killed.
Despite the peace treaty of 1851, Hunkpapa Lakota chief Running Antelope killed four Arikaras in 1853.
Around the same year, a joint Cheyenne and Lakota war party found a big Crow camp in the valley of the Little Bighorn River. The Lakota One Bear killed a Crow woman taken captive by the Cheyennes.
Around 1855, the Assiniboines and the Lakotas met on the battlefield more often than before. The Arikaras conquered horses from the Sioux at least in 1858, while war parties of Crows troubled Lakotas near the Upper Platte the same year.
Though intertribal fighting had existed before the arrival of white settlers, some of the post-treaty intertribal fighting can be attributed to mass killings of bison by white settlers and government agents. The U.S. army did not enforce treaty regulations and allowed hunters onto Native land to slaughter buffalo, providing protection and sometimes ammunition.  One hundred thousand buffalo were killed each year, until they were on the verge of extinction, which threatened the tribes' subsistence. These mass killings affected all tribes thus the tribes were forced onto each other's hunting grounds, where fighting broke out.  
The Lakota continued harassment of the Mandan, Hidatsa and Arikara. By summer 1862, all three tribes had been forced out of their shared treaty territory. "We, the Arikara, have been driven from our country on the other side of the Missouri River by the Sioux", stated chief White Shield in 1864. The elimination of buffalo also meant that the Yanktonai Sioux moved into Assiniboine hunting grounds in North Dakota and Montana, where the Assiniboine made peace with them. 
Before long, the Crows saw their western Powder River area flooded with trespassing Lakotas in search of bison, and "... large scale battles with invading Sioux" took place near present-day city of Wyola, Montana. The outnumbered Crows were little by little displaced. "The country from the Powder River to the Yellowstone River was their country [the Crows'], until 1859, when they were driven from it by the Sioux". In 1868, after a series of battles with the United States army in the contested area, the Lakotas finally succeeded in turning a part of the Crow Indian territory of 1851 into unceded Indian territory of their own.
Later again, huge parts of the different Indian territories would in one way or another be added to the holdings of the United States. Smaller areas of the initial Indian territories became separate reservations, usually populated with Indians from the tribe, which held the treaty right in 1851.
However, the Crow territory provided in the end acreage to two different reservations. The Crow Reservation was created in the center of the original territory in 1868. The reservation of the Northern Cheyennes became a reality in 1884. It is located entirely within the boundaries of the 1851 Crow territory, after the Indians in question had "earned the right to stay in the north" after the Fort Robinson outbreak.
The Arapahoe (Northern Arapaho) settled down on the reservation of their past enemies, the Shoshone, in present Wind River Reservation in Wyoming. The Southern Cheyenne and the Arapaho live in a common reservation in present Oklahoma, also far from their 1851 treaty land.
The Assiniboine in the United States has since 1888 lived in partly Fort Peck Reservation and partly Fort Belknap Reservation, both placed north of the Missouri in present Montana. The treaty territory of the Assiniboine south of the Missouri was just a small portion of the wide range used by these northern plains Indians.
- Indian Peace Commission, which would negotiate the second Treaty of Fort Laramie
- Paragraph 69, Report to The President By The Indian Peace Commission, January 7, 1868
- See e.g. Meyer, Roy W.: The Village Indians of the Upper Missouri. The Mandans, Hidatsas, and Arikaras. Lincoln and London, 1977, p. 186. Sutton, Imre (Ed.): Irredeemable America. The Indians Estate and Land Claims. Albuquerque, 1985.
- Kappler, Charles J.: Indian Affairs. Laws and Treaties. Washington, 1904. Vol. 2, p. 594. http://digital.library.okstate.edu/kappler/Vol2/treaties/sio0594.htm
- Kvasnicka, Robert M. and Herman J. Viola: The Commissioners of Indians Affairs, 1824-1977. Lincoln and London, 1979, p. 43.
- Paragraph 33 Report to the President by the Indian Peace Commission, January 7, 1868
- Kvasnicka, Robert M. and Herman J. Viola: The Commissioners of Indian Affairs, 1824-1977. Lincoln and London, 1979, p. 52 and pp. 49-55.
- "Fort Laramie Treaty of 1851 (Horse Creek Treaty)" (PDF). Retrieved August 28, 2016.
- Harjo, Suzan Shown (2014). Nation to nation: treaties between the United States & American Indian Nations. Washington, DC: Smithsonian Institution.
- Robinson, Doane: Official Correspondence Pertaining to the Leavenworth Expedition into South Dakota in 1823 for the Conquest of the Ree Indians. South Dakota Historical Collections, Vol. 1 (1902), pp. 179-256.
- Stands In Timber, John and Margot Liberty: Cheyenne Memories. Lincoln and London, 1972, p. 162. See also p. 54.
- Fowler, Loretta: Arapahoe Politics, 1851-1978. Symbols in Crises of Authority. Lincoln and London, 1982, p. 56. See also Bass, Althea: The Arapaho Way. A Memoir of an Indian Boyhood. New York, 1966, p. 11. Anderson, Jeffrey D.: One Hundreds Years of Old Man Sage. An Arapaho Life. Lincoln and London, 2003, p. 72.
- Michno, Gregory (2006). "The Indian Trail of Broken Treaties" (PDF). Wild West. p. 40.
With the treaty duly agreed to and signed, the Lakotas promptly went north, and over the next two years, attacked the Crows, invaded their lands in what would become Wyoming and Montana, moved in and drove them out. The Cheyennes joined in the attacks in 1853.
- Paragraph 35 Report to the President by the Indian Peace Commission, January 7, 1878
- Hyde, George E.: Life of George Bent. Written form His Letters. Norman, 1987, pp. 137-163 and 164-222. Hoig, Stan: The Sand Creek Massacre. Norman, 1961.
- See e.g. Bettelyoun, Susan Bordeaux and Josephine Waggoner: With My Own Eyes. A Lakota Woman Tells Her People's History. Lincoln and London, 1998, pp. 53-54. Fowler, Loretta: Arapaho and Cheyenne Perspectives. From the 1851 Treaty to the Sand Creek Massacre. American Indian Quarterly, Fall 2015, Vol. 39, No. 4, pp. 364-390, p. 367.
- Mallery, Garrick: Picture-writing of the American Indians, 10th annual Report of the Bureau of American Ethnology, 1888-89. Washington, D.C., 1893, pp. 572-573. For an exploit by Sitting Bull about two years after the signing of the treaty, see Greene, Candance: Verbal Meets Visual: Sitting Bull and the Representation of History. Ethnohistory, vol. 62, No. 2 (April 2015), pp. 217-240. Picture on page 228.
- Red Cherries' Account to George Bird Grinnell, Envelope 118, George Bird Grinnell Papers. Southwest Museum Library, Los Angeles, page 1.
- McGinnis, Anthony: Counting Coup and Cutting Horses. Intertribal Warfare on the Northern Plains, 1738-1889. Evergreen, 1990, p. 105.
- McGinnis, Anthony: Counting Coup and Cutting Horses. Intertribal Warfare on the Northern Plains, 1738-1889. Evergreen, 1990, p. 90.
- McGinnis, Anthony: Counting Coup and Cutting Horses. Intertribal Warfare on the Northern Plains, 1738-1889. Evergreen, 1990, p. 103.
- Andrew C. Isenberg , The Destruction of the Bison: An Environmental History, 1750-1920 Cambridge University Press, 2000, p. 127
- J. Weston Phippen, 'Kill Every Buffalo You Can! Every Buffalo Dead Is an Indian Gone', The Atlantic, May 13, 2016
- Carolyn Merchant, American Environmental History: An Introduction, Columbia University Press, 2007, p.20
- John C. Ewers, Intertribal Warfare as the Precursor of Indian-White Warfare on the Northern Great Plains, The Western Historical Quarterly, Vol. 6, No. 4 (Oct., 1975), pp. 397-410
- Hunkpapa chief Running Antelope alone killed 17 Arikaras in the years 1853-1865. Mallery, Garrick: Picture-writing of the American Indians, 10th Annual Report of the Bureau of American Ethnology, 1888-89. Washington, D.C., 1893, pp. 572-573.
- Meyer, Roy W.: The Village Indians of the Upper Missouri. The Mandans, Hidatsas, and Arikaras. Lincoln and London, 1977, p. 108.
- Serial 1220, 38th Congress, 2. Session, Vol. 5, House Executive Document No. 1, p. 408.
- John C. Ewers, Intertribal Warfare as the Precursor of Indian-White Warfare on the Northern Great Plains ,The Western Historical Quarterly, Vol. 6, No. 4 (Oct., 1975), pp. 397-410
- Medicine Crow, Joseph: From the Heart of the Crow Country. New York, 1992, p. 84.
- Serial 1308, 40th Congress, 1st Session, Vol. 1, Senate Executive Document No. 13, p. 127.
- Kappler, Charles J.: Indian Affairs. Laws and Treaties. Washington, 1904. Vol. 2, pp. 998-1003. http://digital,library.okstate,edu/kappler/Vol2/treaties/sio0998.htm
- American Memory. Indian Land Cessions in the United States, 1784 to 1894. See the different tribes. http://memory.loc.gov./cgi-bin
- Kappler, Charles J.: Indian Affairs. Laws and Treaties. Washington, 1904. Vol. 2, pp. 1008-1011. (Treaty with the Crows, 1868). American Memory. Indian Land Cessions in the United States, 1784 to 1894. Map: Montana 1. http://memory.loc.gov.
- Weist, Tom: A History of the Cheyenne People. Billings, 1894, p. 84 and p. 104. Serial 4015, 56th Congress, 1st Session, pp. 918-919. Compare the location of the Northern Cheyenn Reservation with the boundaries of the Crow territory of 1851.
- Fowler, Loretta: Arapahoe Politics, 1851-1978. Symbols in Crises of Authority. Lincoln and London, 1982, pp. 66-67.
- Serial 4015, 56th Congress, 1st Session, pp. 852-853.http://memory.loc.gov.
- Kappler, Charles J.: Indian Affairs. Laws and Treaties. Washington, 1904. Vol. 1, pp. 264-265.
- "Treaty of Fort Laramie with Sioux, Etc., 1851." 11 StatsAffairs: Laws and Treaties — Vol. II: Treaties. Washington, D.C.: Government Printing Office, 1904, pp. 594–596. Through Oklahoma State University Library, Electronic Publishing Center.
- Map of North America following the 1851 Treaty of Fort Laramie at omniatlas.com
- National Park Service, Treaties and Broken Promises, retrieved November 23, 2016