Beginning in September of 1913, 10,000 workers for the Colorado Fuel and Iron company went on strike to protest low pay and poor working conditions. Workers constructed a tent camp housing 1200 workers near the company town. On April 19th, 1914, the Colorado National Guard deployed a machine gun overlooking the camp and demanded that the strikers give up. On April 20th, they opened fire killing 25 people, 11 of whom were children.
It always sucks learning about a horrific atrocity that ends with "the perpetrators received zero consequences for their actions and the victims never saw a shred of justice."