It's been a while since I've read about it, but as I recall, tensions were mounting between the Natives and the whites. Many thought, as had often happened, that the Natives would start attacking white settlers again. An attempted arrest of Sitting Bull by Native police officers went wrong, leading to multiple people getting shot to death, including Sitting Bull. When the US military caught up with this group of hundreds of Natives, they started to confiscate their firearms. At some point while this was going on, some kind of Native shaman resisted and several other Natives opened fire on the U.S. military. More Natives started grabbing the confiscated rifles and firing, which led to a huge massacre. It's a pretty fucked up situation all around, but I would say not nearly as cut-and-dry evil as the Ruby Ridge situation. Still really sad that many innocent people ended up getting killed .