The Palmer Raids involved mass detention and deportation without trial. These raids were significant because they happened under Federal authority. US repression certainly involved torture and mass murder previously but mostly done locally (and sure, respond, "that was 'just' done to slaves and indians").

"The individuals captured during the Palmer raids were held in abysmal conditions: at Deer Island, six hundred prisoners were placed in barracks intended to house three hundred, with no heat and dwindling food; many were marched through Boston in chains and handcuffs, showered with the spit and trash of bystanders. In Detroit, eight hundred prisoners were crammed into a windowless corridor with only one working bathroom and no beds. At Ellis Island, hundreds of men were forced to sleep on steel slabs without mattresses."

Edit: Down voted without comment after being upvoted. I seldom reply but this is an exception - cowards!

https://en.wikipedia.org/wiki/Palmer_raids

Two dead and few dozen ill doesn't quite sound like the worst thing. Random street cops do that to more people for no good reason in any given year.

Those are all conspiracy theories. ;)