Animosity between union organizers and mining operators hit a boiling point in August 1913 after the callous murder of union organizer Gerald Lippiatt by mine guards. The Colorado Fuel & Mining Company (CFI) did not acknowledge the murder and local authorities refused to investigate. Angered by their inaction, the United Mine Workers of America (UMWA) District 15 gathered at Trinidad to declare a strike on September 16. The union demanded recognition, a ten percent wage increase, enforcement of eight-hour workday laws, checkweighmen to verify the payment per ton of coal, payment in cash, freedom to buy and sell, and enforcement of all other mining laws. When their demands were announced on September 23, retribution was swift.
Before the day was out, all miners and their families had been evicted from company housing and left without means to buy food and other goods. To aid them, the UMWA provided half a dozen tent colonies, the largest of which were at Aguilar and Ludlow.
For a month, spurts of violence interrupted the lull in negotiations. The Baldwin-Felts Agency, anti-union mercenaries employed by the mining operators, sent in strikebreakers from West Virginia to harass the strikers and break the union. The detectives drove around in machine-gun equipped cars and assaulted the Forbes tent colony, killing a striker and a small boy. However, the strikers were not guiltless either. They continually harassed non-union miners (“scabs”) who continued to work, threatening them and their families if they refused to join the strike. Civil conditions rapidly deteriorated in the region, culminating in the murder of company guard John Nimmo. It was at that moment that CFI president L.M. Bowers begged Colorado Governor Elias Ammons to send in the National Guard to restore order.
Governor Ammons declared martial law in the coalfields, and militiamen under the command of General John Chase arrived in late October. Their arrival, however, only intensified the violence. An official government report described the militiamen as the “very scum of humanity” for their unwarranted assaults on women, children, and enslavement of captured strikers. General Chase vehemently denied those accusations, insisting that the actions of the National Guard were legal necessities to prevent unnecessary loss of life. By the time the strike ended in May 1914, an estimated 150–200 people had been killed or severely maimed.