The Colorado Coalfield War was a major labor uprising in the southern and central Colorado Front Range between September 1913 and December 1914. Striking began in late summer 1913, organized by the United Mine Workers of America (UMWA) against the Rockefeller-owned Colorado Fuel and Iron (CF&I) and other corporate mining enterprises after years of deadly working conditions and low pay. According to the 1915 U.S. Commission on Industrial Relations Report on the Colorado Strike, "The struggle in Colorado was primarily a struggle against arbitrary power, in which the question of wages was secondary, as an immediate issue". The strike was marred by both targeted and indiscriminate attacks from both strikers and individuals hired by CF&I to defend its property. Fighting was focused in the southern coal-mining counties of Las Animas and Huerfano, where the Colorado and Southern railroad passed through Trinidad and Walsenburg. It followed the 1912 Northern Colorado Coalfield Strikes.