I respectfully submit you prediction has come true at least two times already:
Here’s a couple more:
July 28, 1932 - Washington DC (Bonus Soldiers)
May 31, 1921 - Tulsa OK (State-sponsored race riot)
July 1316, 1863 - New York City Draft Week (over 1200 killed)
There was another in which 40 Italian Americans were openly executed in the either the 1890’s or 1900’s, but I can’t nail down an exact date.
And those are just a few.
don’t forget Kent State