Libertarians think that only defensive war is justified.  This belief about war is an extension of the beliefs about individual violence. Just as persons cannot permissibly attack other persons, so nations cannot permissibly attack other nations.  The late Harry Browne’s statement is representative:

Most libertarians believe you shouldn’t initiate force against someone who has never used force against you. Force is to be used only in self-defense — not used just because you don’t happen to like someone, or because someone doesn’t like you, or because he might become dangerous in the future, or because some third party has attacked you and you want to prove you’re not a wimp. The same principles must apply to our nation — that it shouldn’t use force against a nation that hasn’t attacked us.

I’d like to explain why this line of reasoning is problematic (I expand on a previous post.) Let us start by accepting the impermissibility of aggressive interpersonal violence. This rule has a corollary: the permissibility of defensive violence. If someone initiates aggression against me, I am entitled to defend myself. Now defensive violence includes not only defense of self but also defense of others. Suppose I’m passing by and see a villain (Attacker) assault a defenseless person (Victim). Surely I have the right to defend Victim by using force against Attacker. Victim’s defensive rights are transferable to me. (I assume other requirements for permissible violence are met: Victim is innocent, Attacker is culpable, Victim has consented to my defending her, and my response is proportionate. On these and other matters see Larry Alexander’s discussion.)

Let us now transpose this reasoning to war. Most libertarians say that defensive war is justified. How so? Because a defensive war is the use of violence by persons who have been unjustly attacked by a foreign army. Under the libertarian principle of nonaggression, if the evil enemy invades we may permissibly defend ourselves and our fellow citizens (also victims of the attack) against the attackers. This means that my violence against the attackers is an action both in self-defense and defense of others. And the government’s job is to coordinate our defensive actions. Many views of the state (including libertarian views) list this defensive role as a raison d’être of the state.

If this analysis is correct, then it turns out that a defensive (and therefore justified) war is a war in defense of persons, self and others. It is not a defense of the state or the government per se. We can generalize by saying that, for the libertarian, the only justified violence is violence in defense of persons (self and others) who are victims of unjust attacks. Wars waged to achieve territorial aggrandizement, national glory or dominance, or similar non-defensive reasons, are never justified.

Now take Rwanda, April-June 1994. One ethnic group, the Hutus, attacked another ethnic group, the Tutsis, and in a 100 days killed about 800,000 of them (See the account here.) Now suppose the United States could have stopped this genocide at a low cost to everyone except the attackers because, say, their primitive machetes could not rival American advanced weapons.  Standard libertarian doctrine says that this would have been an offensive war, an initiation of violence against Rwanda.  Since neither Rwanda nor the Hutus would have attacked the United States, the United States would not have had any business intervening in Rwanda. It would have been an unjustified war.

But this cannot be right, if we accept the legitimacy of defense of others. The action of the United States in this hypothetical is analogous to the action in the example above of defending Victim against Aggressor. The distinction between defensive and offensive wars is misleading because it treats the state as a “person” who can be Attacker or Victim. But states are not persons. When we (correctly) disaggregate the state, what we have is a group of human beings unjustly attacking another group of human beings. A defense of the victim here is not an offensive war: it is a defensive war, a war in defense of unjustly-attacked persons. As such, it should not be banned by the libertarian principle that condemns the offensive use of violence.

Of course, problems remain. First, as Bryan Caplan has argued, empirical and epistemic considerations may lead us to oppose any war, even defensive ones. I accept this arguendo, as my only purpose is to show that if those epistemic barriers could be overcome, then interventions to protect persons from genocide could in principle be justified under the libertarian principle of nonaggression and its corollary, the permissibility of defending others.

Second, unlike what happens in many individual cases, in most wars innocent bystanders die. It could be then argued that war, but not individual defense of others where there is no collateral harm, is banned precisely because it inflicts collateral harm. This is a serious problem that philosophers of war have tried to address by invoking, controversially, the Doctrine of Double Effect and similar devises. All I would say here is that this objection proves too much. For in the defensive war that the libertarian does allow (a reaction against the invader) there is collateral harm as well. We kill innocent women and children when we repel the aggressor. So if the reason to oppose the war in defense of unjustly-attacked persons in Rwanda is that it kills innocent bystanders, then the libertarian has to oppose the use of violence in our own defense as well.

Finally, it may be argued that our government has a limited mandate: to protect ourselves and our territory and nothing more.  This fiduciary duty prohibits the government to use our resources to defend others, even in Rwanda-like cases. Defending Tutsis is just not part of the government’s job description. This view may be subject to possible objections about the relative stringency of moral duties to save others if we can do so at a reasonable cost, but I accept it arguendo. Interestingly, this view renounces the attempt to ground libertarian pacifism on the nonaggression principle. Foreign wars are banned, not because they are impermissible initiations of violence, but for a different reason, namely that the government is not authorized to defend others. This position would have to accept the private organization of volunteers to defend the genocide victims in Rwanda. This position is also consistent with contractual arrangements to defend others. Imagine that a government proclaims that from now on it will abide by the libertarian principle of nonaggression. The government announces that it will not initiate any military action for any reason other than defending actual victims of unjustified attacks. The government inserts a clause to that effect in all enlistment contracts. This would authorize enlisted soldiers to refuse to participate in any war that was not a defense of persons against unjustified attacks. Such an arrangement, I believe, would be consistent with sending forces to Rwanda to stop the genocide.

Maybe we should be pacifists. Maybe the danger that governments will abuse their war powers, even where strictly limited to self-defense or defense of others, should make us wary of accepting even national self-defense, let alone defense of others. (To me, that is hard to stomach, and I’m glad we didn’t recoil from defending unjustly-attacked persons in World War II.) All I tried to show here is that the libertarian opposition to foreign wars cannot be based on the distinction between defensive and offensive wars. Only the defense of persons, self or others, (sometimes) justifies war. This includes some foreign wars.