Nineteen men

The Ludlow Massacre was a mass killing perpetrated by anti-striker militia during the Colorado Coalfield War. Soldiers from the Colorado National Guard and private guards employed by Colorado Fuel and Iron Company (CF&I) attacked a tent colony of roughly 1,200 striking coal miners and their families in Ludlow, Colorado, on April 20, 1914. Approximately 21 people were killed, primarily miners' wives and children. John D. Rockefeller Jr. was a part-owner of CF&I who had recently appeared before a United States congressional hearing on the strikes, and he was widely blamed for having orchestrated the massacre.