By Wanjiru Njoya, Mises Wire | September 01, 2026
In the Ethics of Liberty, Murray Rothbard argued that aggressive war is always immoral and must always be opposed. The just war doctrine should be understood not as a moral toolkit that can be harnessed to justify aggressive war, but, on the contrary, as an exception to the foundational anti-war principle. This means that the just war exception should never become more important than the anti-war rule.
Unfortunately, many now treat the just war doctrine as a presumption that launching war is morally upstanding so long as a “just cause” can be found to rationalize it. The prevailing ideology of war—even though it waves aloft the traditional just war criteria—has departed from the anti-war standard. The new presumption is pro-war. The pro-war lobby acts as if all they need is a good excuse, a “righteous cause,” to justify their aggressive wars.
In his “Just War” article Rothbard explained how the prevailing international law of war “that has been dominant since 1914, by the dominant partisans of the League of Nations and the United Nations” subverted the traditional principles set out by “the classical international natural lawyers.” Warmongers have pitched their tent on the moral high ground:
. . .the modern interventionists have won by seizing the moral high ground; theirs is the cosmic “humanitarian” path of moral principle; those of us who favor American neutrality are now derided as “selfish,” “narrow,” and “immoral.” In the old days, however, interventionists were more correctly considered propagandists for despotism, mass murder, and perpetual war, if not spokesmen for special interest groups, or agents of the “merchants of death.” Scarcely a high ground.
In Rothbardian ethics, the starting point of the just war doctrine must always be the rule against aggressive violence. The principles set out in the Ethics of Liberty to prohibit aggression between individuals, Smith and Jones in Rothbard’s example, apply to states too: “The same criteria hold if Smith and Jones each have men on his side, i.e. if ‘war’ breaks out.”
If violence between Smith and Jones is wrong, violence does not become morally acceptable merely because Smith and Jones have rallied more men to help them fight. Rothbard emphasized that “the rule prohibiting violence against the persons or property of innocent men is absolute; it holds regardless of the subjective motives for the aggression.” The aim in applying the same rule to states is “to reduce the degree of coercion exercised by States over individual persons as much as possible.”
As readers will be aware, Rothbard’s political philosophy is grounded in natural law and natural rights. In his “Just War” article, he emphasized that the reason why classical natural-rights international law required war always to be justified was to drive home the point that war is presumptively wrong—“war, as a grave act of killing, needs to be justified.”
The just war criteria were not intended as some sort of template, in the sense that if you can shoehorn an intended war into the criteria that gives you the green light to wage war with impunity. Since there is always bound to be injustice somewhere or other in the world, there is always a putative reason for states to be in a perpetual state of war—it is for “humanitarian” purposes, or to spread human rights and democracy. Rothbard cautionedthat such endless war is very tempting for any state which has constituted itself as a perpetual “army on the march”:
In war, therefore, the State frantically mobilizes the people to fight for it against another State, under the pretext that it is fighting for them. Society becomes militarized and statized, it becomes a herd, seeking to kill its alleged enemies, rooting out and suppressing all dissent from the official war effort, happily betraying truth for the supposed public interest. Society becomes an armed camp, with the values and the morale—as Albert Jay Nock once phrased it – of an “army on the march.”
The Ethics of Liberty also addressed the case of a revolutionary war: “Does opposition to all inter-State war mean that the Libertarian can never countenance change of geographical boundaries—that he is consigning the world to a freezing of unjust territorial regimes? Certainly not.”
The applicable principle is that of voluntary association, or nations by consent. The just war doctrine constitutes the principled foundation of self-defense in the context of nations. In the Ethics of Liberty, Rothbard gave the example of an aggressive state, Walldavia, unjustly annexing the Western territory of a neighboring state, Ruritania. Ruritanians in the annexed region are now unjustly forced to be citizens of Walldavia. He arguedthat, even in the face of this injustice, “We must still maintain the illegitimacy of the Ruritanian State’s mounting a war against Walldavia.” Any other rule would put the citizens of Walldavia at risk of suffering violence for an aggressive decision made by the warmongers who govern their state.
This does not mean the besieged Ruritanians must forever suffer under oppression. They are entitled to revolt.
The legitimate routes to geographical change are (1) revolutionary uprisings by the oppressed Western Ruritanian people, and (2) aid by private Ruritanian groups (or, for that matter, by friends of the Ruritanian cause in other countries) to the Western rebels—either in form of equipment or volunteer personnel.
The point here is that although the annexation of Ruritanian territory is unquestionably unjust, it does not follow that the state of Ruritania is justified in launching war against Walldavia. Peaceful resolution is always to be preferred. The fact that injustice abounds in the world does not mean states would be justified in launching wars to correct those injustices.
Further, even in cases where war is justified, it does not follow that anything done in furtherance of the just cause is acceptable. In his “Just War” article, Rothbard highlighted two principles from the classical theory—first, “above all, don’t target civilians” and second, “preserve the rights of neutral states and nations” who choose not to get involved.
Drawing upon classical international natural law offers the distinct advantage of universality. Its principles transcend any particular war or historical epoch, governing all men at all times and in every situation. There are no “special rules” for special people who are more entitled than others to wage aggressive wars.
Yet this very universality carries a notable drawback—the term “universal” is frequently taken to imply that any state bears a moral duty to intervene in support of a just cause anywhere in the world, treating the grievances of one as the grievances of all humanity. We are accustomed, when Ruritania is annexed, to show our solidarity by saying “we are all Ruritanians now” and symbolically flying the Ruritarian flag.
Rothbard rejects that type of political “solidarity with the oppressed” as grounds for war. He clarifies that the universality of the ethics of liberty does not imply a duty to intervene in any war. In “Just War” he explains:
Many of my friends and colleagues are hesitant to concede the existence of universal natural rights, lest they find themselves forced to support American, or worldwide intervention, to try to enforce them. But for classical natural-law international jurists, that consequence did not follow at all. . . . We might encapsulate this position into a slogan: “Rights may be universal, but their enforcement must be local,” or, to adopt the motto of the Irish rebels: Sinn Fein, “ourselves alone.” A group of people may have rights, but it is their responsibility, and theirs alone, to defend or safeguard such rights.
Those who wish to support the quest for independence are free, of course, to do so in their personal capacity. William Prescott Frost Jr.—father of the famous New England poet Robert Lee Frost—is a great example. As a young boy in 1862, he set off for the South to join the Army of Northern Virginia. Alas, he only got as far as Philadelphia before he was intercepted and sent back home to Massachusetts. But in making up his own mind to support the Peace Democrats, who opposed Lincoln’s War, he exemplified a very Rothbardian ethical principle.
Dr. Wanjiru Njoya is the Walter E. Williams Research Fellow for the Mises Institute. She is the author of Economic Freedom and Social Justice (Palgrave Macmillan, 2021), Redressing Historical Injustice (Palgrave Macmillan, 2023, with David Gordon), “You Stole Our Land: Common Law, Private Property, and Rothbardian Principles of Justice” (Journal of Libertarian Studies, 28 (1): 91–119 (2024) and “Individual Liberty, Formal Equality, and the Rule of Law” (Palgrave Handbook of Classical Liberalism, forthcoming, 2026).
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