Despite attempts to suppress union activity, the United Mine Workers of America secretly continued its unionization efforts in the years leading up to 1913.
Eventually, the union presented a list of seven demands:
Recognition of the union as bargaining agent
Compensation for digging coal at a ton rate based on 2,000 pounds (previous ton rates were of long tons of 2,200 pounds)
Enforcement of the eight-hour work-day law
Payment for "dead work" (laying track, timbering, handling impurities, etc.)

Weight checkmen elected by the workers (to keep company weightmen honest)
Right to use any store, and to choose their boarding houses and doctors
Strict enforcement of Colorado's laws (such as mine safety rules, abolition of scrip), and an end to the company guard system
The major coal companies rejected the demands.
In September 1913 the United Mine Workers of America called a strike.
Those who went on strike were evicted from their company homes and moved to tent villages prepared by the union.
The tents were built on wood platforms and furnished with cast-iron stoves on land the union had leased in preparation for a strike.

When leasing the sites, the union had selected locations near the mouths of canyons that led to the coal camps in order to block any strikebreakers' traffic.
The company hired the Baldwin–Felts Detective Agency to protect the new workers and harass the strikers.

Baldwin–Felts had a reputation for aggressive strike breaking.
Agents shone searchlights on the tent villages at night and fired bullets into the tents at random, occasionally killing and maiming people.
They used an improvised armored car, mounted with a machine gun the union called the "Death Special", to patrol the camp's perimeters.
The steel-covered car was built at the Colorado Fuel & Iron Company plant in Pueblo, Colorado, from the chassis of a large touring sedan.
Confrontations between striking miners and working miners, whom the union called scabs, sometimes resulted in deaths.
Frequent sniper attacks on the tent colonies drove the miners to dig pits beneath the tents to hide in.
Armed battles also occurred between (mostly Greek) strikers and sheriffs recently deputized to suppress the strike: this was the Colorado Coalfield War.

As strike-related violence mounted, Colorado governor Elias M. Ammons called in the Colorado National Guard on October 28.
At first, the Guard's appearance calmed the situation, but the Guard leaders' sympathies lay with company management.
Guard Adjutant-General John Chase, who had served during the violent Cripple Creek strike 10 years earlier, imposed a harsh regime.
On March 10, 1914, a replacement worker's body was found on the railroad tracks near Forbes, Colorado.
The National Guard said the strikers had murdered the man.
In retaliation, Chase ordered the Forbes tent colony destroyed.
The attack was launched while the residents were attending a funeral of two infants who had died a few days earlier.
Photographer Lou Dold witnessed the attack, and his images of the destruction often appear in accounts of the strike.

The strikers persevered until the spring of 1914.
By then, according to historian Anthony DeStefanis, the National Guard had largely broken the strike by helping the mine operators bring in non-union workers.
The state had also run out of money to maintain the Guard, and Ammons decided to recall them.
He and the mining companies, fearing a breakdown in order, left one company of Guardsmen in southern Colorado.
They formed a new company called "Troop A", which consisted largely of Colorado Fuel & Iron Company mine camp guards and mine guards hired by Baldwin–Felts, who were given National Guard uniforms.
Despite attempts to suppress union activity, the United Mine Workers of America secretly continued its unionization efforts in the years leading up to 1913. Eventually, the union presented a list of seven demands:
Recognition of the union as bargaining agent
Compensation for digging coal at a ton rate based on 2,000 pounds (previous ton rates were of long tons of 2,200 pounds)
Enforcement of the eight-hour work-day law
Payment for "dead work" (laying track, timbering, handling impurities, etc.)
Weight checkmen elected by the workers (to keep company weightmen honest)
Right to use any store, and to choose their boarding houses and doctors
Strict enforcement of Colorado's laws (such as mine safety rules, abolition of scrip), and an end to the company guard system
The major coal companies rejected the demands. In September 1913 the United Mine Workers of America called a strike. Those who went on strike were evicted from their company homes and moved to tent villages prepared by the union. The tents were built on wood platforms and furnished with cast-iron stoves on land the union had leased in preparation for a strike.
When leasing the sites, the union had selected locations near the mouths of canyons that led to the coal camps in order to block any strikebreakers' traffic. The company hired the Baldwin–Felts Detective Agency to protect the new workers and harass the strikers.
Baldwin–Felts had a reputation for aggressive strike breaking. Agents shone searchlights on the tent villages at night and fired bullets into the tents at random, occasionally killing and maiming people. They used an improvised armored car, mounted with a machine gun the union called the "Death Special", to patrol the camp's perimeters. The steel-covered car was built at the Colorado Fuel & Iron Company plant in Pueblo, Colorado, from the chassis of a large touring sedan. Confrontations between striking miners and working miners, whom the union called scabs, sometimes resulted in deaths. Frequent sniper attacks on the tent colonies drove the miners to dig pits beneath the tents to hide in. Armed battles also occurred between (mostly Greek) strikers and sheriffs recently deputized to suppress the strike: this was the Colorado Coalfield War.
As strike-related violence mounted, Colorado governor Elias M. Ammons called in the Colorado National Guard on October 28. At first, the Guard's appearance calmed the situation, but the Guard leaders' sympathies lay with company management. Guard Adjutant-General John Chase, who had served during the violent Cripple Creek strike 10 years earlier, imposed a harsh regime. On March 10, 1914, a replacement worker's body was found on the railroad tracks near Forbes, Colorado. The National Guard said the strikers had murdered the man. In retaliation, Chase ordered the Forbes tent colony destroyed. The attack was launched while the residents were attending a funeral of two infants who had died a few days earlier. Photographer Lou Dold witnessed the attack, and his images of the destruction often appear in accounts of the strike.
The strikers persevered until the spring of 1914. By then, according to historian Anthony DeStefanis, the National Guard had largely broken the strike by helping the mine operators bring in non-union workers. The state had also run out of money to maintain the Guard, and Ammons decided to recall them. He and the mining companies, fearing a breakdown in order, left one company of Guardsmen in southern Colorado. They formed a new company called "Troop A", which consisted largely of Colorado Fuel & Iron Company mine camp guards and mine guards hired by Baldwin–Felts, who were given National Guard uniforms.
Ludlow Massacre