The Ludlow Massacre? Been to that site.Your correct, but it was a military unit.
Here are a few examples of the US Army being used in the past and modern times which is whitewashed but true. Some incidents have been left out of this link.
6 Times the Military Was Used for Riot Control in the US
When local law enforcement can't restore law and order, the US military gets the call.www.military.com
I'll look up the massacre in Colorado and some others shortly.
OSA should be able to figure out a way to blame the union for that one.