The terms of the Treaty that created the Great Sioux Reservation were negotiated in 1868. The Sioux reneged on the treaty every bit as much as the US government did. Several of their chiefs claimed both the land of the reservation, and the right to continue to come and go, hunt, trap, make war with other tribes, and kill settlers wherever they pleased, despite the fact that the treaty required them to assent to the reservation system.
They wanted to eat their cake, and still have it for later.
When they left their reservation to make war on the Crow Nation and started murdering settlers, they started a war. As a result of that war, they lost 7.7 million acres of their country.
Happens all the time. Saying that land is "disputed" is like saying the US Southwest is "disputed" or that the land the Israelis took in the Six Day War is "disputed." No it isn't. The Sioux lost the Black Hills in a war they started, and a war they lost.
In any event, as I said “get off my lawn!” is not going to work.
And the Black Hills gold rush of 1874 had nothing whatsoever to do with this?!