Wounded Knee (the second one not the original one) was 1973.
Kent State in '70. The Bonus Army (homeless WWI vets) in the 30s. Blair Mountain (coal miners on strike) and the Tulsa Race Massacre in '21.
Only a half dozen times in the last 100 years or so.
Uh, no? "An eye for an eye." is old school ancient.
It was however a limiting statement. When Hammurabi made "an eye for an eye" into law, it meant you couldn't just go kill a man's entire family over losing an eye and call it justified.