The two treaties being exercised are the 1851 & 1868 Treaties of Fort Laramie.
The Treaty of Fort Laramie (also the Sioux Treaty of 1868[b]) was an agreement between the United States and the Oglala, Miniconjou, and Brulé bands of Lakota people, Yanktonai Dakota and Arapaho Nation, following the failure of the first Fort Laramie treaty, signed in 1851.
The treaty formed the basis of the 1980 Supreme Court case, United States v. Sioux Nation of Indians, in which the court ruled that tribal lands covered under the treaty had been taken illegally by the US government, and the tribe was owed compensation plus interest. As of 2018 this amounted to more than $1 billion. The Sioux have refused the payment, demanding instead the return of their land.
If you want more information about the treaties, here are some resources.
- Full text of the 1851 Treaty
Indian affairs: laws and treaties, Vol. 2, page 589(Treaties)
- Full text of the 1868 Treaty of Fort Laramie
Indian affairs: laws and treaties, Vol. 2, page 588(Treaties)
- Extensive list of Treaty Violations with historical context