I was reading something about this a while back. If I remember correctly one of the causes was a failure to supply the Sioux with food. I believe one official's comment was " They can eat grass."
Yes, it was largely about the massive corruption centered on the Indian agent, Thomas Gailbraith. Little Crow's people were getting a third of what they needed and it was rotten, buggy and tampered with. Liquor was being brought in and it was the old firewater - cayenne pepper, tobacco juice (spittoons), whatever they decided. The cash tribe had been promised was a no-show. Let them eat grass was indeed said and that's why the government men were found with grass stuffed in their faces. (This same thing was said by Northrup about Andersonville when he heard complaints - 'The Yankees can eat grass.")
Just a few years before this, California lit up with 'Indian troubles' from north to south. Only recently have historians been acknowledging the depth of corruption in the government agents...some of whom actually tried to do away with their charges with poison! Like the Sioux Uprising, the Modoc War was brought on by abusive government policies and corrupt (even psychotic) agents.
This affair put Lincoln in a sorry spot. He knew there was rot in the Indian affairs department but he had no idea of how massive it really was. A preacher finally bent his ear about it and the president was appalled. He promised to do something about it but had a bigger war to fight at the moment so it had to wait. After his assassination, Johnson did nothing - he, too, had other things to worry about - but eventually Grant did try. He set Ely Parker up as head of the Bureau of Indian Affairs, which was under military control, and set up his strangely naive Peace Policy to largely replace the pirates who passed as agents with religious folks.
Well, the people who rose up got the heavy hand of the law on their heads and a far less number were hanged than wanted. The people wanted every single Indian killed, period, and would have been delighted if the army had swept through and annihilated all. (This was one of the reasons a large number of Chippewa, Ojibway and Huron people signed up for the Union - show loyalty. The locals had a tendency to kill the nearest people handy, not the guilty!) I give Lincoln credit for going over the paperwork for each and every one of the Indians accused and filtering it down to around 36. But he couldn't win for losing. He ordered the remainder of Little Crow's people across the Missouri to a marshy land full of disease and nearly all his band died. All the Dakota were expelled from Minnesota. (Whenever somebody is expelled or removed from somewhere...it isn't just them!)
This was the start of the long and very involved US-Dakota Conflict which ended at Wounded Knee in 1890. Officially, anyway...
www.history.com
