Seizure of the Black Hills

The United States government illegally seized the Black Hills – a mountain range in the US states of South Dakota and Wyoming – from the Sioux Nation in 1876. The land was pledged to the Sioux Nation in the Treaty of Fort Laramie, but a few years later the United States illegally seized the land and nullified the treaty with the Indian Appropriations Bill of 1876, without the tribe's consent.

Source: Wikipedia — Seizure of the Black Hills (CC BY-SA 4.0)