A Short History of Just War

by | 15 Mar 2022

Roman Priest (Louvre Museum, Public domain, via Wikimedia Commons)

Reading British newspapers’ commentary on the Ukraine war gives a sense of deja vue. We have a return of the ‘West’, of the ‘Free World’, of the exreme demonisation of the opponent. Commentators are urging NATO to send troops to Ukraine, to institute a no-fly zone, to become militarily actively.  Ukraine needs NATO’s ‘humanitarian’ intervention, the postmodern version of the old concept of just war. This short article discusses the history of just war.

Throughout history, people have gone to wars and sacrificed themselves for religion, empire, nation or ideology. Religious and secular leaders know well the importance of adding high principle to low ends. This is equally evident in Homer’s Iliad, in Thucidides’ chilling description of the Athenian atrocities at Melos and Mytilene, in the chronicles of the crusades and in the films about the Iraq and Afghanistan wars. Stalin’s use of religious themes in the defence of the Soviet Union against the Nazis in 1941, despite decades of religious persecution, is a typical of the cynical moral turn often taken by rulers. Such cynicism has been treated with wry smiles by writers and poets. Shakespeare as much as Brecht were fascinated by the way in which the hawks of war put on the fleece of moralist and preacher, better to  persuade soldiers and citizens about the value of killing and dying for the cause. As the poet Wyndam Lewis put it ‘but what war that was ever fought, was an unjust war, except of course that waged by the enemy’.

This moralisation of war is relatively easy when the moralisers are victims of aggression. But empire builders, colonialists, the Αmericans in Iraq and the Russians in Ukraine are not devoid of moral rhetoric. Putin claims that he invaded Ukraine to save the Russian speakers from ‘genocide’, the accusation that the Ukranian leadership levels agains the Russians. The hawks of war have always put on the fleece of moralist and preacher, to  persuade soldiers and citizens about the value of killing and dying for the cause.

The lack of a moral arbiter has made just war one of the hardest moral mazes. For the warring parties, there is nothing more certain than the morality of their cause. For third parties, there is nothing more uncertain than the rightness of the combatants’ conflicting moral claims.  War is always morally ambiguous. This ambiguity  becomes evident in the history of the morally justified or ‘just’ war. 

In premodern societies, no law of war existed. Their customs determined the correct way for starting the war, the conduct of war and the treatment of hostages and the dead. It is against this background of moral undecidability that we must examine the history of the morally justified or ‘just’ war.  In premodern societies, war was a natural and undisputed part of political organisation. No formal law of war existed, but the customs of tribe or polis determined the correct way for starting the war, the conduct of war and the treatment of opponents, hostages and the dead. The Iliad, the Trojan Women or Antigone offer ample evidence of such customs. It is not true therefore that legally unregulated warfare is unlimited warfare. Every community develops its own rules and customs for conducting this ultimate test of life.

The formal concept of the bellum justum appeared in Rome. Before the beginning of hostilities, the fetials, a college of priests, determined whether the conditions for going to war existed, and then performed certain legal and religious practices: A jus fetiale, a legal demand for just satisfaction, was issued and was followed by auguries taken before battle. Gods decided the outcome of battles and wars. The scrupulous observance of rituals was a good insurance policy. The ancient practices of war brought together sacral functions, religious rituals and legal regulation. All three are still with us today.

The early Church developed first a consistent theory of just war in an attempt to serve Caesar without abandoning totally its pledges to God. The Church father Augustine argued that a just war redresses a moral wrong and restores the violated moral order.

It has three characetristics

1. It must be declared by legitimate authority as a last resort.

2. it must have justa causa. Wars were just if conducted in self-defence or for restitution and retribution after unjust acts or conquests.

3. the it should have a reasonable prospect of success.

Medieval theology became preoccupied with the definition of the justice of the cause,  the lawful initititation of war known as jus ad bellum. It neglected the jus in bello (the lawful conduct of war).  The divine duty to punish infidel and evil-doers made the prosecution of war limitless. We had the unremitting violence of the Crusades, the genocidal attacks on Indians and indigenous people of the New World

All this came to an end in the 17th and 18th centuries with the emergence of early international law, the Jus Publicum Europaeum. The law secularised the idea of the just cause and started developing a legal regulation of war.  The theologians had assumed that only one of the warring parties could be just, as it would be contradictory for both to pursue a just cause. They determined the justice of the cause from God’s perspective. Lawyers, fancy themselves as a priesthood, but they could not claim god’s onniscience.  International law abandoned the search for universal standards of justice. The sovereign states were the only judges of their cause. Both parties could believe unreasonably but validly that their cause is just.

Emphasis shifted from the cause of war to the development of a detailed jus in bello, legal rules to regulate the conduct of war without overburdening the parties with excessive concern for the collateral damage of their action. The principle of discrimination distinguishes between military staff and civilian populations and prohibits attacking, targeting or otherwise harming non-combatants except when absolutely necessary. The principle of proportionality, attempts to adjust the means and scope of military action to its legitimate objectives.

The undermining of the theological conceptions of just war, replaced morality with sovereignty. The judgement that a war is just belongs exclusively to the sovereign.  By declaring and waging war, the sovereign accomplishes its nature. Similarly, the jus in bello, the law of war, is a sovereign concession and implicit contract amongst princes, an exception to the Roman maxim has it inter armes silent leges in war the law is silent.  Immanuel Kant, who wanted war abolished despised this laywerly pragmatism, attacked Grotius, the father of international law, as a ‘miserable comforter’ of Kings. For Kant reason condemns war; the ideal should be not just war but just peace. Force can be used morally in very few instances. The aim of cosmopolitan society, first evangelised by Kant, was defined negatively: it is the abolition of war.

The European legal regulation depended on two crucial exceptions: in the colonial wars against savages  and heathen, the constraints of the law of war, premised on a society of homogeneous christian sovereigns, did not apply.  The so-called European ‘amity line’ dictated a certain civility in metropolitan wars.  The new world on the other hand became the space of release of European barbarity. In a related development, the idea of the ‘enemies within’ emerged and was strengthened by the rise of nationalist and racist ideologies. For the modern ideological state, radical political and social opposition is seen as a challenge the internal ordre publique.  Indeed, while Plato had stated that it is an abominable outrage for the parties in civil war to ravage the lands or burn the houses of the other, something acceptable in a war against strangers, modernity has reversed the situation.  War is partly regulated while civil war has no limits. Dissidents and rebels are treated as as bandits, terrorists, subhuman subject to annihilation.

The early modern theory of just war was the clearest sign of the emergence of a new system of law and international relations based on state sovereignty.  Beyond its immediate aims, war’s purpose is to accomplish the essence of the sovereign. A war between sovereigns is just because the combatants are formally equal actors (hostes aequalitur justi).

Just War in the Twentieth Century

The twentieth century changed somewhat this picture. After the world wars, the desire not just to control but to prevent war returned. The first count in the Nuremberg indictment was for crimes against peace, in other words, the crime of waging unjust war. Under Chapter 7 of the UN charter, war became unlawful unless it is in self-defence or on the authorisation of the Security Council acting on its obligation to prevent and stop violations of peace. In this sense, just war theory returned, partly masked in the distinction between aggressive and defensive wars.  But the picture was complicated by the fact that the post-WWII legal order was based on two contradictory principles. A claim to universal human rights, was schizophrenically accompanied by the principle of non intervention in the internal affairs of states, in other words the inviolability of sovereignty.

In the long Cold War period, most wars involved either the two superpowers or their satelites. As a result, the UN Security Council (“SC”) was unable to attract the unanimous view of the permanent members for military intervention. The attempt to codify in law crimes against peace failed.  A legal definition of just war would be a double-edged sword for the Major Powers. But after the fall of communism an extensive moral order emerged with a weak legal gloss, human rights and humanitarianism. The aim is to moralise domestic and international politics. According to international lawyer Ruti Teitel a new ‘humanity’s law’ has emerged. It brings together the law of war and human rights law.  The most obvious sign of this new moralism is the emergence of humanitarian wars, where military force has been placed in the service of humanity. Bosnia Kosovo and Libya were early examples of this new military humanitarianism.

Let me discuss briefly two examples about attitudes to saving populations. When Vietnam invaded Cambodia in 1978 and overthrew the Khmer Rouge regime, today accepted as the worst case of genocide in the second part of the twentieth century. with the 2 million dead of the Killing Fields, it was universally condemned. The French said that “[t]he notion that because a régime is detestable foreign intervention is justified and forcible overthrow is legitimate is extremely dangerous. That could ultimately jeopardize the very maintenance of international law and order” A Soviet veto prevented a SC resolution ordering the Vietnamese to withdraw.

Look at Rwanda in 1994: despite evidence was presented to the SC about an imminent genocide, the council withdrew the existing UN peacekeepers except for 270 French soldiers. When a resolution was proposed to the effect that a genocide was taking place, putting into effect emergency measures under the Genocide convention, the British representative said that calling what was happening a genocide would make the SC a laughing stock.

In the same year 1994, NATO forces started bombing Serbian positions in Bosnia.

The Responsibility to Protect (r2p)

The UN intervention in Bosnia-Herzegovina was carried out under SC mandate. The NATO bombing of Kosovo and Yugoslavia in 1999 was different. Milocevic and the government of Serbia were attacking and ethnically cleansing Albanians from the southern province of Kosovo.  To stop that, NATO systematically bombed for the first time since WWI Belgrade, a major European capital. Kosovo was an extensive use of military force for humanitarian purposes without SC authorisation. Morality was reintroduced into war unilaterally.

After the  end a major effort was launched to develop a new theory of just war. The debate is whether morality can inform law’s role of regulating the most extreme form of politics, war. The great achievement of modern law is precisely the proclaimed exclusion of morality from its operations. The experience of the murderous religious wars, of the relativism of values in a multicultural sociaity and the fear of nihilism meant that modern law sees itself as a neutral mechanism. Morals, ideology or politics should be kept out of it, to allow law to turn social conflict into technical questions about the meaning of rules and entrust it for resolution to rule experts, lawyers and judges. But then as we know you can never keep the buggers out. The contortions of the relationship between politics, law and morality bedevilled the attempt to define humanitarian war after Kosovo.  

The first to try a comprehensive definition was Tony Blair. Following his championing of ethical foreign policy, he formulated five criteria of postmodern just wars In a Chicago speech: Are we sure of our case? Have we exhausted all diplomatic options? Are there military operations we can sensibly and prudently undertake? Are we prepared for the long term? Do we have national interests involved? The most interesting omission is international law; the most striking innovation, the insertion of national interest. International law would come back and torment Blair when the legality of the imminent Iraq war became a political issue. The addition of national interest was more revealing. National interest, a palpable contradiction if not refutation of moral principle, reveals the postmodern just war logic.  It allows cases to be distinguished from pressing precedents, while insisting that the moral motives for (in)action are fully adhered.  Human rights and humanitarianism offer the gloss of moral universalism without the discipline of moral consistency. This combination of moral stringency and utilitarian laxity makes the millenarian ambitions of humanitarianism the perfect cover for empire and, national interest, the perfect imperial opt-out clause.

Senior Western international lawyers agreed that the Kosovo war that the use of force was a grave illegality but had a moral justification. The war was illegal but legitimate. But this was an one off unrepeatable case, it did not create a precedent. Jurgen Habermas, the putative heir to Kant, and our own muscular liberals disgreed. Kosovo showed the way forward by pushing international law towards its cosmopolitan phase and upholding universal citizenship rights. For the lawyers, moral considerations must be introduced because international law in its amorality declares the war illegal. The law on its own is inadequate to the task of saving humanity.  Habermas poses the problem and its answer in reverse terms. The law of human rights properly extended can save the day. For the lawyers, morality saves politics from (inadequate) law. For Habermas, the law saves politics from (potentially problematic) moralisation.

Following this stalemate, an International Commission on Intervention and State Sovereignty concluded in 2001 that states have a responsibility to protect their population and the international community must assist them. International lawyers agreed that the Kosovo use of force was a grave illegality but had a moral justification. The war was illegal but legitimate. But this was an one off unrepeatable case, it did not create a precedent. The International Commission on Intervention and State Sovereignty concluded in 2001 that states have a responsibility to protect their population and the international community must assist them. The r2p, as it became known, was eventually adopted by World Summit of the UN in 2005.

The international community may use sanctions and military intervention as a last resort if a state fails to protect its population from genocide, crimes against humanity, war crimes and ethnic cleansing. However the use of force must be authorised by the SC as has always been the case. It is the Security Council with the inbuilt veto power of the 5 permanent members that must authorise intervention.

In 2011 the UN Security Council authorized for the first time a military intervention in Libya using r2p terminology. It authorized Member States to take “all necessary measures” to protect civilians but it explicitly rejected regime change. The three permanent states driving the intervention (the US, UK and France, or “P3”) quickly moved to support the anti-Gaddafi forces however.  It soon led to chaos and heavy civilian casualties.  The BRICS—Brazil, Russia, India, China and South Africa, all then represented on the Council—argued that the protection mandate was exceeded. When we came to Syria, President Obama insisted in 2013 that the goal of any intervention would be to protect citizens and not “regime change or harm unarmed citizens. Russia and China vetoed the resolution to use violence in Syria. They stated that R2P had been abused by the U.S. as a pretext for ‘regime change’ in Libya. India, Brazil and South Africa agreed and even the British Parliament voted against the use of force.

We are returning to the intimate connection between strategic priorities and moral concerns. A few months before the Iraq war, while on a lecture tour of China, I asked a high ranking Chinese official if China would exercise its veto.  He replied that his country has no interests in Iraq and by supporting the US expects to be rewarded in trade relations and its own human rights difficulties. A few days later China abstained and immediatley afterwards joined the WTO, a long ambition. Morality and human rights are wheeled out when they supports state interests and are easily discarded if they create real or imaginary constraints.

I don’t want to deny that the arguments from international law have value. But from a wider perspective, they miss the point: in our wars against terrorists and barbarians, the role of international law is not to decide its initiation but to help its legitimacy.  Morality exists if it is effective and military action is moral if it succeeds.

Let me conclude. War and just war theories have been important strategies for the emergence of state sovereignty. War brings states to life, literally as most states have been the outcome of war or revolution, metaphorically by energising nations and metaphysically by raising people to the universal through their confrontation with death. War has always acted as the litmus test for man and nation. ‘War is to men as maternity to women’ stated Mussolini.

A ‘humanitarian’ war is a contradiction in terms.  War and its consequences, bombing and maiming people can never be moral. Bombing does not protect people and does not prevent atrocities. A destructive war, by definition a devastating negation of human rights, can be seen as humanitarian only because human rights are often hijacked by governments and politicians, those against whom they were invented.


  1. An excellent Begriffsgeschichte from CD. Let’s try to bring it up to the present. Russia’s recent escalation of its intervention in Ukraine is an instance of R2P, at least that part of the casus belli which involves protecting the civilians of the Donbas, especially the Russian-speaking population under attack by Ukrainian nationalists. With the difference from the Libyan case in that, as of NATO countries’ decision to intervene in Libya, the threat posed to civilians in the rebel areas of Benghazi and elsewhere in eastern Libya in winter-spring 2011 was demonstrably smaller than that of the civilian toll in eastern Ukraine from 2014 to 2022. The “denazification” rationale also invoked by the Russia federation is also an extension of R2P doctrine. And like NATO humanitarian imperialism in 2011, predictably, a limited-scope operation can quickly expand into an event of constitutive-destructive monumentality: regime change and interminable civil war in Libya or, in the Ukrainian case, a potentially world-order altering event. The non-Atlanticist countries on the UNSC, incl. Russia and China, who allowed the resolutions on Libya to pass in 2011– the scope of authorization was so vague and broad it couldn’t but be abused — deserve some blame for naiveté, at best, and/or opportunism.

  2. Stalin called to patriotism and not religion. It was Russian patriotism and not religious factor that pushed 27 millions of Soviet to sacrifice themselves and to finally defeat nazism and fascism in europe and elsewhere. in Ukraine war, it is not the USSR that is fighting neo nazism but Russians threatened once again by the advance of Kiev’s neo nazi regime on their borders. In the case of the ongoing Ukraine war, we cannot speak of juste war but of special military operations to disarm and to denazify Ukraine used by western imperialism as pawn and tool against Russia. there is no declaration of war of Russia against Ukraine. Author’s views are mainly legalist callig to the law and not to Geopolitical rivalries and chiefly to western imperialism which is at the origin of wars since the sabotage of a genuine socialist successful experience in the USSR and eastern Europe.


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