did this nation have enemies?
Yes, the American troops.
Arapaho
Several skirmishes had ignited hatred from the "white" folk that lived in the area, and left Arapaho and Cheyenne tribes in constant fear of being attacked by American troops. 
what were the terms of the treaty of fort laramie why did it fall One of the terms was that  it established the Great Sioux Reservation including ownership of the Black Hills, and set aside additional lands as "unceded Indian territory" in areas of South Dakota, Wyoming, and Nebraska, and possibly Montana. It failed as neither parties fully honored the terms. who was this treaty signed by? The United States and the Oglala, Miniconjou, and Brulé bands of Lakota people, Yanktonai Dakota and Arapaho Nation. what is the language spoken by the last nation you mentioned? The Arapaho language.
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Arapaho [SEP] Events Leading to the Sand Creek Massacre
Several skirmishes had ignited hatred from the "white" folk that lived in the area, and left Arapaho and Cheyenne tribes in constant fear of being attacked by American troops. For example, on April 12, 1864, a rancher brought troops to attack a group of 15 warriors who had asked for reward from bringing his mules back to him. The warriors acted in self-defense, and sent the troops running. Word got back to Colonel John Chivington, and they had told him the Indians shot first. He also heard there were 175 cattle head stolen from the government. Chivington "ordered troops to find and 'chastise' the 'Indians'.