Background: Rockefeller was the second of six children and eldest son born in Richford, New York to con artist William Avery "Bill" Rockefeller (November 13, 1810 - May 11, 1906) and Eliza Davison (September 12, 1813 - March 28, 1889). His siblings were Lucy (1838-1878), William Jr. (1841-1922), Mary (1843-1925) and twins Franklin (Frank) (1845-1917) and Frances (1845-1847). His father was of English and German descent while his mother was of Scots-Irish descent. Bill was first a lumberman and then a traveling salesman who identified himself as a "botanic physician" and sold elixirs.
Context: The strike, called in September 1913 by the United Mine Workers, over the issue of union representation, was against coal mine operators in Huerfano and Las Animas counties of southern Colorado, where the majority of CF&I's coal and coke production was located. The strike was fought vigorously by the coal mine operators association and its steering committee, which included Welborn, president of CF&I, a spokesman for the coal operators. Rockefeller's operative, Lamont Montgomery Bowers, remained in the background. Few miners actually belonged to the union or participated in the strike call, but the majority honored it. Strikebreakers (called "scabs") were threatened and sometimes attacked. Both sides purchased substantial arms and ammunition. Striking miners were forced to abandon their homes in company towns and lived in tent cities erected by the union, such as the tent city at Ludlow, a railway stop north of Trinidad.  Under the protection of the National Guard, some miners returned to work and some strikebreakers, imported from the eastern coalfields, joined them as Guard troops protecting their movements. In February 1914, a substantial portion of the troops were withdrawn, but a large contingent remained at Ludlow. On April 20, 1914, a general fire-fight occurred between strikers and troops, which was antagonized by the troops and mine guards. The camp was burned, resulting in 15 women and children, who hid in tents at the camp, being burned to death. Costs to both mine operators and the union were high. This incident brought unwanted national attention to Colorado.  Due to reduced demand for coal, resulting from an economic downturn, many of CF&I's coal mines never reopened and many men were thrown out of work. The union was forced to discontinue strike benefits in February 1915. There was destitution in the coal fields. With the help of funds from the Rockefeller Foundation, relief programs were organized by the Colorado Committee on Unemployment and Relief. A state agency created by Governor Carlson, offered work to unemployed miners building roads and doing other useful projects.  The casualties suffered at Ludlow were successfully labeled a massacre and mobilized public opinion against the Rockefellers and the coal industry. The United States Commission on Industrial Relations conducted extensive hearings, singling out John D. Rockefeller Jr. and the Rockefellers' relationship with Bowers for special attention. Bowers was relieved of duty and Wellborn restored to control in 1915, then industrial relations improved. Rockefeller denied any responsibility and minimized the seriousness of the event. When testifying on the Ludlow Massacre, and asked what action he would have taken as Director, John D. Rockefeller stated, "I would have taken no action. I would have deplored the necessity which compelled the officers of the company to resort to such measures to supplement the State forces to maintain law and order." Rockefeller admitted that he had made no attempt to bring the militiamen to justice.
Question: What was the strike of 1913-14?

Answer:
The strike, called in September 1913 by the United Mine Workers, over the issue of union representation, was against coal mine operators in