The history of labor unions in America is written largely from a Marxist perspective, which is based on the assumption of capitalist exploitation of labor. The true is quite different.
For example, take a look at this history of the coal mine violence in West Virginia:
http://vi.uh.edu/pages/buzzmat/Radhistory/radical%20history%20articles/West%20Virginia%20Mine%20Wars%20WW%20I%20Era.pdf
If anything, the violence escalated because of the failure of the government to defend private property. Consider, a strike means that the labor union uses violence to prevent the employer from hiring replacement workers to continue operations. The government ignores this violation of private property and instead supports the labor union’s false claim to a right to the jobs of its members. When the employer uses force to evict labor union members from his property and employ replacement workers, the government, again, stands by and allows the union to escalate the violence.
Here’s more to read, in general, about the failure of government in labor relations:
http://www.independent.org/issues/google_results.asp?cx=018225991961863933630%3Awvyquibswjc&ie=UTF-8&cof=FORID%3A11&q=labor+unions
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