Because the indigenous people, I hate using the terms “Indian” or even “Native American”, were here long before the European settlers came and stole the land from them. After the US became a nation and after many years of conflicts between the native people and the settlers, the Federal government decided to set aside land for these indigenous people and made the natives sign treaties allowing them to live on these reservations. Many of these treaties were later broken by the federal government and forced them to live on often smaller reservations in less hospitable locations.

One of these treaties and what I consider one of the most egregious cases involves the Sioux nation of tribes and the Black Hills of South Dakota, that the federal government originally thought was worthless land but later gold was found in the Black Hills and the government decided they wanted that land back. You can read about it on Wikipedia at: Black Hills land claim - Wikipedia and you can watch a 2011 PBS report about at: Why the Sioux Are Refusing $1.3 Billion. By the way, that estimated $1.3 billion in 2011 sounds like a lot of money but if that was divided up equally between all the members of the Sioux Nation would have only been about $10,000 each.