Labor unrest in the United States in the years preceding World War I was particularly tense in the West, where coal miners had been trying to organize and join the UMWA. When a union activist was killed in the fall of 1913, workers at the Colorado Fuel and Iron Corporation, finally went on strike on September 23 to protest low wages ($1.68 a day) and poor working conditions. This provoked a harsh response from the Rockefeller family, which controlled the company and effectively ruled the region. Since the company owned the towns where the workers lived, it was able to evict strikers from their homes, leaving women and children, mostly from immigrant families, without shelter as the harsh Rocky Mountain winter approached. Helped by UMWA groups across the country, the strikers were able to organize tent cities and carried on their strike, often with violent means.
At first, the company responded by hiring a private detective agency to harass the strikers. Despite a number of deaths, the workers refused to give in and Colorado governor Elias M. Ammons called in the National Guard. Even though the campaign of harassment increased and many of the organizers were beaten and arrested, the miners persevered and managed to survive the winter under the most severe conditions. By April, 1914, the governor finally decided to evict the tent cities that sprang up around the mines, even though these had been established on public property.
On the morning of April 20, the National Guard opened fire with machine guns on the tent city of Ludlow, the largest of the tent cities, located 18 miles north of Trinidad, Colorado. The miners fired back, and the assault seemed to be leading nowhere, so a ceasefire was organized and one of the union organizers, Louis Tikas, was sent to the National Guard to arrange a truce. He was killed by the soldiers shortly after he arrived there, and the assault on the tent city continued. A total of thirteen people were shot dead during the incident. The day was originally being celebrated as Easter by the many Greek immigrants among the strikers.
As night approached, the militia descended on the tent camp and set fire to it, not knowing that two women and eleven children had been hiding beneath a cot and did not escape with the other strikers. When their charred bodies were found the next day, their deaths became a rallying cry for the UMWA, who called the incident the "Ludlow Massacre."
News of the event spread across the country overnight. Armed workers from the surrounding tent cities converged on the camp to fight the National Guard, railway workers and other unions began strikes in sympathy with the coal miners, and even some National Guardsmen refused to fight against the strikers. In Congress, Socialist representative Victor Berger of Wisconsin called on all workers to get guns to defend themselves. After ten days of fighting, Governor Ammons finally called on President Woodrow Wilson to intervene. Federal troops were sent to the region and all the strikers and National Guardsmen were disarmed. In the end, the strikers failed to obtain their demands, their union did not obtain recognition, and union workers were replaced by non-union ones. None of the National Guardsmen who attacked the strikers was ever prosecuted, though sixty-six people had died in the violence by the time the strike finally ended.