Just War Theory Explained

  • “We must not conceal from ourselves that no improvement in the present depressing situation is possible without a severe struggle; for the handful of those who are really determined to do something is minute in comparison with the mass of the lukewarm and the misguided. And those who have an interest in keeping the machinery of war going are a very powerful body; they will stop at nothing to make public opinion subservient to their murderous ends.” –Albert Einstein; Mein Weltbild
  • War is defined as: a state of conflict between two or more sovereign nations carried on by force of arms.”1  Just War Theory is derived from Christian tradition, although all major religious faiths have expressions about the legitimacy of war.
  • St. Augustine developed the origins of Just War Theory. He contended that one’s own life or property was never a justification for killing one’s neighbor. Christian charity was the motivating force behind this statement. But when one speaks of rulers of nations they have the obligation to maintain peace. This obligation gives them the right to wage war. He says, “‘The natural order conducive to peace among mortals demands that the power to declare and counsel war should be in the hands of those who hold the supreme authority.”
  • Fundamentally, the philosophy of Just War is about three things:
    1. Taking Human Life is Wrong and Should Be Avoided
    2. States have a duty to defend their citizens and justice
    3. Protecting innocent human life and defending important values sometimes requires the use of violent force
  • The aim of Just War Theory is to provide a guide to the right way for states to act in potential conflict situations. It only applies to states, and not to individuals
  • The theory is not intended to justify wars but to prevent them, by showing that going to war except in certain limited circumstances is wrong, and thus motivate states to find other ways of resolving conflicts.
  • Just War Theory is divided into two fundamental parts, Jus ad bellum (Law to War) and Jus in bello (law in war)

Jus Ad Bellum

Justice to War

  • War can only be waged for a just cause, such as self-defense against an armed attack.
  • War can only be waged under legitimate authority. Usually the constitution and the laws of a nation state specify the institutions and personnel authorized to make war decisions. The U.N Charter authorizes the Security Council to make the international community’s war decisions. Citizens at their own will cannot attack another country without the permission of the legitimate authority. Conversely, in a democratic nation state, statesmen with legitimate authority will need to convince citizens that their course of action is legal and proper.
  • War can only be waged with the right intention. Correcting a suffered wrong is considered a right intention, while material gain is not. Thus a war that would normally be just for all other reasons would be made unjust by a bad intention. Right intention requires that democratic statesmen accept the decision of their nations’ courts and electorates on the legitimacy and the justice of their action. Augustine said, “’The passion for inflicting harm, the cruel thirst for vengeance, an unpacific and relentless spirit, the fever of revolt, the lust of power, and such things, all these are rightly condemned in war.’2
  • War can only be waged with a reasonable chance of success. It is considered unjust to meaninglessly waste human life and economic resources if defeat is unavoidable.
  • War must be waged with proportionality in mind. The suffering which existed pre-war should not be overshadowed by the suffering the war may cause.
  • War can only be waged as a last resort. War is not just until all realistic options which were likely to right the wrong have been pursued.

Jus in Bello

Justice in War

  • Just war conduct should be governed by the principle of discrimination. The acts of war should be directed towards the inflictors of the wrong, and not towards civilians caught in circumstances they did not create. The prohibited acts include bombing civilian residential areas that include no military target and committing acts of terrorism or reprisal against ordinary civilians. Some theologians believe that this rule forbids weapons of mass destruction of any kind, for any reason (such as the use of an atomic bomb).
  • Just war conduct should be governed by the principle of proportionality. The force used must be proportional to the wrong endured, and to the possible good that may come. The more disproportional the number of collateral civilian deaths, the more suspect will be the sincerity of a belligerent nation’s claim to justness of a war it initiated.
  • Torture, of combatants or of non-combatants, is forbidden.
  • Prisoners of war must be treated respectfully.
    • Many throughout history have considered conscription an unjust means, e.g.
    • “It is debasing human dignity to force men to give up their life, or to inflict death against their will, or without conviction as to the justice of their action.” — Albert Einstein, Mahatma Gandhi in the “Manifesto Against Conscription and the Military System”

Jus post Bellum

Justice after War

  • Proportionality and Publicity. The terms of the peace agreement must be public and fair. The victor should not seek to utter destroy the opposing country, but to secure a just peace. In general, this rules out insistence on unconditional surrender.
  • Rights Vindication. The settlement should secure those basic rights whose violation triggered the justified war. The relevant rights include human rights to life and liberty and community entitlements to territory and sovereignty. This is the main substantive goal of any decent settlement, ensuring that the war will actually have an improving affect.
  • Discrimination. When imposing terms on the defeated, one must treat the leaders, soliders, and citizens of the defeated nation individually and appropriately. It would not be just to punish the people of a nation for the actions of its leadership, and soliders should be treated in accordance with their freedom of action. This policy does not excuse soliders from potential punishment for war crimes.
  • Just Punishment When the defeated country has been a blatant, rights-violating aggressor, proportionate punishment must be meted out. The leaders of the regime, in particular, should face fair and public international trials for war crimes. Soldiers also commit war crimes. Justice after war requires that such soldiers, from all sides to the conflict, likewise be held accountable to investigation and possible trial.
  • Compensation. Financial restiution may be demanded, to pay for the costs of the war, but it would not serve justice to impoverish the defeated country.
  • Rehabilitation. Following the war, the victor may impose reforms on the defeated government, proportional to its level of abuse and corruption. They may involve: demilitarization and disarmament; police and judicial re-training; human rights education; and even deep structural transformation towards a minimally just society governed by a legitimate regime.

Criticism of Just War Theory

  • Pacifism. Because Just War Theory allows for potential scenarios when war is permissible, some pacifists believe is serves as a justification for war as often as it serves as an obstacle to it.
  • Moral Nihilism with Respect to War. The “All’s Fair in Love and War argument” contends that it is impossible to apply moral precepts to acts of war. This philosophy is best exemplified by the German philosopher Karl von Clausewitz, who wrote in his classic work On War:
    • War is therefore a continuation of policy by other means. It is not merely a political act but a real political instrument…. What still remains peculiar to war relates merely to the peculiar character of the means it employs.
    • He continues, “Philanthropic souls may imagine that there is a way to disarm or overthrow our adversary without much bloodshed…. Agreeable as it may sound, this is a false idea which must be demolished.… We can never introduce a modifying principle into the philosophy of war without committing an absurdity.
  • Necessity/Inevitability of War
    • This is perhaps best exemplified by the work of Machiavelli, who wrote:
    • “Here is a just cause; iustum enim est bellum quibus necessarium, et pia arma ubi nulla nisi in armis spes est.” And “necessary”, for Machiavelli, meant necessary to the growth, expansion, and glory of the state.3


  1. John A. McHugh, O.P. and Charles J. Callan, O.P., Moral Theology: A Complete Course, vol. 1 (New York: Joseph F. Wagner, 1929), 545.
  2. Thomas Aquinas, Summa Theologica, vol. 3, IIaIIaeQQ. 1-148, trans. by the Fathers of the English Dominican Province (Westminster, Maryland: Christian Classics, 1981), 1354.
  3. Kenneth Kemp, Department of Philosophy, University of St. Thomas, “Just War Theory and Its Non-Pacifist Rivals, 2002
  4. “War ().” Stanford Encyclopedia of Philosophy. 11 Feb. 2009 <http://plato.stanford.edu/entries/war/>.
  5. Aquinas, St Thomas. (1988). Politics and Ethics. Norton.
  6. Norman, Richard (1995). Ethics, Killing, and War.


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