(From:
http://en.wikipedia.org/wiki/Monopoly_on_violence )
Max Weber said in Politics as a Vocation that a necessary condition for an entity to be a state is that it retains such a monopoly. His expanded definition was that something is "a 'state' if and insofar as its administrative staff successfully upholds a claim on the monopoly of the legitimate use of violence (German: das Monopollegitimen physischen Zwanges) in the enforcement of its order."[1] [2]
According to Weber, the state is the source of legitimacy for any use of violence.[citation needed] The police and the military are its main instruments, but this does not mean that only public force can be used: private force (as in private security) can be used too, as long as it has legitimacy derived from the state.
Weber applied several caveats to this basic principle.
Weber intended his statement as an observation, stating that it has not always been the case that the connection between the state and the use of violence has been so close. He uses the examples of feudalism, where private warfare was permitted under certain conditions, and of Church courts, which had sole jurisdiction over some types of offenses, especially heresy (from the religion in question) and sexual offenses (thus the nickname "bawdy courts").
The actual application of violence is delegated or permitted by the state. Weber's theory is not taken to mean that only the government uses violence, but that the individuals and organizations that can legitimize violence or adjudicate on its legitimacy are precisely those authorized to do so by the state. So, for example, the law might permit individuals to use violence in defense of self or property, but in this case, as in the example of private security above, the ability to use force has been granted by the state, and only by the state.
One implication of the above is that states that fail to control the use of coercive violent force (e.g., those with unregulated militias) are essentially not functional states. Another is that all such "functional" states function by reproducing the forms of violence that sustain existing social power relationships, and suppressing the forms of violence that threaten to disrupt them.