Paul Johnson's Modern Times devotes a chapter to this: http://www.amazon.com/Modern-Times-Revised-Edition-Perennial...
In general, private armies, political assassinations, and other forms of political violence seldom lead to good outcomes: other examples would be Lebanon during and prior to the civil and (not to Godwin this) Weimar Germany with government-funded but ruthless and private and political Freikorps, as well as KPD/SPD/NSDAP/etc... paramilitary organizations. Finally, if a government enacts and enforces laws and decrees contrary to the constitution and human rights in general (i.e., it is no longer a constitutional state), introduction of political gives government forces both an excuse and the means to start acting fully extra-judicially.
I'll note that I'm saying this as a individual with classical liberal/libertarian political leanings and as a strong supporter of a right to bear arms. My view is shared with by David Friedman, an anarcho-capitalist (a view that I don't subscribe to, but respect): http://econlog.econlib.org/archives/2013/07/in_case_of_revo....