Libertarianism is generally associated with what is traditionally called an “isolationist” stance in matters of international relations. At the extreme edge, the anarcho-capitalists regard all states, of whatever form and function, as intrinsically evil. Therefore, they (following Rothbard) tend to see little distinction between the desirability of living under the authority of one state relative to others, and their foreign policy prescription will be to simply to devolve all states, while urging what is virtually a pacifist foreign policy.
Even those libertarians who accept the necessity of the minimal state (such as Ron Paul, I think) tend to be deeply suspicious of what they regard as foreign policy adventurism. Their regard international military bases, foreign aid, and defensive alliances like NATO as unwise and not in the best interest of the citizens of the U.S. The general idea seems to be that peace-loving states should respond militarily only to direct attacks on their territory or to other unambiguous acts of war (e.g. unjustified naval blockades, attacks on vessels in international waters, etc.). Let us call such provocations “classic causes of war” or “CCW” for short.
This policy is typically justified on a number of grounds, including the possibility of harm to innocent civilians or neutral parties; the cost of maintaining a military capacity consistent with non-CCW missions; the damaging economic effects of war; the general incompetence and venality of state officials; and the tendency of the authorities to use armed conflict as an excuse to encroach on civil liberties. While all of these considerations are reasonable, and not to be dismissed casually, none of them represent a decisive moral argument against non-CCW interventions, particularly if there is a strong countervailing reason for undertaking such missions.
In other words, assuming that non-CCW actions can be justified from the moral perspective, the arguments in favor of a purely defensive stance do not appear to rule out such interventions on a categorical basis. Is there, then, a legitimate moral basis for non-CCW interventions, and what are the practical benefits? I believe the answer is found in the state of nature analysis offered by John Locke.
Note first that the international sphere closely resembles Locke’s state of nature because there is no single power that can claim a monopoly on the legitimate use of force. Rather, there are a large number of states, all acting in what they perceive to be their self-interest, with varying degrees of ruthlessness and willingness to resort to unprovoked violence. Locke held that in a state of nature any peaceful party may justly punish those who violate the natural rights of other people, even though the aggressor has not specifically acted against him/her. He reached this conclusion on the grounds that an unpunished aggressor represents a clear and present danger to the entire community. See Second Treatise, Chap. III, sec. 16-8. I think Locke’s reasoning is sound.
An unconstrained aggressor imposes two serious costs on those who wish to abide by what Locke called the law of nature, i.e. showing due regard for the equal rights of other persons. First, a party willing to take the life or property of one innocent victim is not likely to stop there. Accordingly, criminals cause fear in even those not directly harmed by their aggression.
Second, the persistence of criminality imposes significant material costs on peaceful parties. Because of the anxiety referenced above, blameless persons will be required to beef up security for themselves and their loved ones. Individuals wishing to conduct mutually-beneficial trade may be prevented from doing so because the goods or the payment will be stolen. Farmers may not plant crops because thieves will seize the harvest, and so on.
Given these considerations, if peace-lovings persons in an idealized state of nature are entitled to punish a criminal who has not attacked them directly, then it also seems clear that they may band together in defensive alliances to deter, resist or punish aggressors in a coordinated way. On this same logic, the right to punish and deter aggression (with military alliances, bases, etc.) should also apply to peaceful contemporary states, that also operate in a lawless environment.
Having said this, it is obviously the case that great care must be taken in exercising this right for the reasons noted above. Just because we have just cause to punish, form defensive alliances, etc. there may be a variety of prudential reasons why we should elect not to do so. Thus, I regard the foreign policy question as essentially one of cost/benefit analysis, and reject the idea that there is any doctrinaire libertarian foreign policy prescription.
The above analysis does not consider the justifiability of non-CCW interventions on humanitarian grounds, which I will leave for another occasion. Obviously, the above discussion only at best scratches the surface of this subject, and much more needs to be said. Thus, as always, I welcome all thoughtful comments.