People always talk about the oppression as ancient history, but it has been perpetual for many groups, not just limited to indigenous. Allotment ran until 1934, giving away native lands. After that they moved to Termination, where they tried to dissolve reservations and negate treaties.
You wanna hear something horrifying? No? Too bad!
The 3rd largest nuclear accident in human history happened on US soil, but it wasn't Three Mile Island. A tailings pond used by a United Nuclear Corporation uranium mill broke and released over 1,000 tons of nuclear material and nearly 100m gallons of contaminated water into the Puerco river and surrounding land.
The disaster happened in Church Rock, New Mexico a few months after TMI occurred, so it should have had national attention since nuclear accidents were still fresh in everyone's minds. However, most people don't know about it. Why? Because it happened next to a Navajo reservation, and the people primarily effected were Navajo. The US government pretended it didn't happen until the 1990s, and refused to clean it up until the early 2000s. In the meantime, cancer and diabetes have skyrocketed in a community without any genetic history of the diseases, the dust on the reservation has become contaminated and blown all over the place.
Oh yeah, and the UNC built another tailings pond, but this time they decided not to line it so now the groundwater is contaminated too.
Some more info here