Conversation so far:
What was the strike of 1913-14 in relation to John D. Rockefeller?
The strike of 1913-1914 was spurred by a unionization effort against John D. Rockefeller's Colorado Fuel and Iron Company's working conditions.
What was the result of the stike of 1913-1914 in Colorado?
The strike of 1913-1914 resulted in miners being displaced and living in tent cities adjacent to mining towns.
What was the Ludlow Massacre?
The Ludlow Massacre was a massacre by the Colorado National Guard and Colorado Fuel and Iron Company guards attacking a tent colony of 1,200 striking coal miners and their families.

Question: Why did this happen?
Self-contained rewrite: Why did the Ludlow Massacre happen?