Private defense agency  A private defense agency (PDA) is a theoretical enterprise which would provide personal protection and military defense services to individuals who would voluntarily contract for its services. PDAs are advocated in anarcho-capitalism. A PDA is distinguished from a private contractor of the state which is subsidized financially through taxation or legally through monopoly and immunity. Instead, such agencies would in theory be voluntarily financed primarily by competing insurance and security companies. As proponents of free-market anarchism, Benjamin Tucker and Gustave de Molinari first explicitly proposed for-profit private defense agencies. The concept later was advanced and expanded upon by anarcho-capitalists who consider the state to be illegitimate, and therefore believe defense is something that should be provided or determined privately by individuals and firms competing in a free market. The Mises Institute published a book of essays entitled "". Murray N. Rothbard in "" and David D. Friedman in "The Machinery of Freedom" expand substantially on the idea. Both hold that a PDA would be part of a privatized system of law, police, courts, insurance companies and arbitration agencies who are responsible for preventing and dealing with aggression. In this environment, victimless crimes and "crimes against the state" would be rendered moot, and the legal realm would be limited to contractual disputes and tort damages, as from assault, burglary, pollution, and all other forms of aggression. This concept is similar to Polycentric law. Within economics, discussion of the concept largely has been confined to the Austrian School, as in Hans Hoppe's article "The Private Production of Defense" published by the Mises Institute. These authors emphasize that PDAs have different motives from existing statist defense agencies. Their survival depends on quality of service leading to a wide customer base, rather than the ability to extract funds via the force of law, as is true of states. Customers and markets would thus dictate that PDAs minimize offensive tendencies and militarization in favor of a pure defense. Anarcho-capitalists believe such privatization and decentralization of defense would eliminate the credibility of, and popular support for, the state. As a private firm offering individually determined defense, the PDA provides a model for how an entirely private defense would work in a free market. John Frederic Kosanke argues that the need for large-scale defense is minimized in direct inverse proportion to the extent of domestic control by the state. He believes that since the greater number of proprietors makes surrender more costly to an aggressor than a relatively authoritarian region, vulnerability to attack is less likely.