The Mine War was the product of three convergent factors: poor working conditions, a rapid influx of immigrants from eastern and southern Europe after 1890, and a major depression beginning in spring 1893. While strikes in the Midwest coalfields had been commonplace since 1887, the depression heightened tensions and the presence of so many new immigrants made common labor action difficult. Many did not speak English and, having no previous understandings with management, were more prone to violence in waging strikes. Wage reductions in April 1894 led the United Mine Workers of America (UMWA) to call for a strike.
The main goal of the strike was not higher wages per se, but rather a reduction of the supply of coal nationwide to drive up coal prices and thereby wages. In this respect, the suspension of production was supported by some mine operators. Although the UMWA had a membership of only 13,000 at the time, around 170,000 bituminous coal miners throughout Illinois, Indiana, Ohio, and Pennsylvania, Maryland, Virginia, and West Virginia answered the call. Because the UMWA was not strong enough to enforce suspension of production in all fields—most notably in Maryland, Virginia, and some parts of Pennsylvania—coal continued to reach the market. Widespread use of nonunion miners led to violent confrontations. Vandalism of mines and railroads became common, and mine owners frequently brought in Pinkerton detectives or local and federal law officers to prevent lawlessness. As conditions worsened, state militias were called out to halt the violence. The mine war was largely a failure. Wages were only slightly adjusted, and the bituminous coal market remained unstable.
By June 1894, the division between old and new miners had become prominent, with some recent immigrant groups taking control of local actions. Although miners were not strictly divided along ethnic lines, violence came to be increasingly associated with anarchism and other radical European ideas. By the mid-1890s, many old immigrants were voting for Populist candidates who were calling for immigration restrictions. Also, old-line groups such as the UMWA began to lobby Congress for an end to immigration.