Just War Theory: Modern vs Classical vs Revisionist vs Pacifism

Modern Just War Theory (JWT) is a secular, normative ethical framework in philosophy, ethics, international relations, and military studies. It evaluates when resorting to war is morally justifiable, how war should be conducted ethically, and (increasingly) how a just peace should be established afterward. It aims to minimize unnecessary suffering, especially to civilians, while rejecting both absolute pacifism (war is never justified) and realism (war is beyond moral judgment).

Unlike classical JWT (rooted in theology and figures like St. Augustine and Thomas Aquinas), the modern version revived prominently in the 20th century. It responded to nuclear weapons, the Vietnam War, and later events like 9/11 and asymmetric conflicts (e.g., terrorism, drones, humanitarian interventions). It secularized the tradition, universalized it beyond Christian contexts, and aligned it with human rights, international law (e.g., UN Charter, Geneva Conventions), and individual accountability. It treats war as a moral problem requiring systematic principles rather than divine sanction or pure state interest.

Three Categories of Criteria of Modern JWT

Modern JWT distinguishes three interconnected but independent categories of criteria (all must generally be satisfied for a war or action to be fully just):

1. Jus ad Bellum (Justice of Resorting to War) — Criteria for when it is right to initiate or enter war:

• Just cause: Typically self-defense against aggression, or humanitarian intervention to stop grave evils (e.g., genocide, massive human rights violations). Not for conquest, revenge, or minor insults.
• Legitimate (or competent) authority: Must be declared by a proper public authority (usually a state government), not private actors or dictators acting illegitimately.
• Right intention: Aimed at achieving justice or peace, not self-aggrandizement, hatred, or ulterior motives.
• Last resort: All reasonable non-violent alternatives (diplomacy, sanctions) exhausted.
• Reasonable prospect of success: Avoids futile bloodshed; hopeless causes are generally impermissible (though moral stands may be exceptions).
• Proportionality: Anticipated benefits (e.g., ending aggression) must outweigh expected harms and costs.

2. Jus in Bello (Justice in the Conduct of War) — Rules governing how war is fought, independent (in traditional views) of whether the war itself is just:

• Discrimination (or distinction/non-combatant immunity): Deliberately target only combatants (those posing a direct threat); civilians and non-combatants must be protected. Indiscriminate attacks (e.g., area bombing of cities) are prohibited. “Double effect” allows foreseeable but unintended civilian harm if it is not the goal and is proportionate.
• Proportionality: Military actions must not cause excessive harm relative to the concrete military advantage gained.
• Military necessity: Force used only as required to achieve legitimate objectives; no inherently evil means (e.g., torture, rape, poison).

3. Jus Post Bellum (Justice After War) — A more recent modern addition (emphasized since the late 20th/early 21st century) for terminating war justly:

• Fair peace terms, reconstruction, reparations (proportionate and non-punitive toward innocents).
• War crimes trials, rehabilitation of aggressors, environmental remediation, and efforts toward lasting reconciliation without undue humiliation.

Modern JWT Proponents (Post 1900)

• Michael Walzer (traditionalist/orthodox): His ‘Just and Unjust Wars’ (1977) is the foundational modern text. It revived and secularized the theory with historical examples, defended the moral equality of combatants, non-combatant immunity, and intervention in extreme cases (e.g., humanitarian). It separates ad bellum from in bello judgments.
• Brian Orend (traditionalist-leaning): Builds on Walzer; defines JWT as a coherent system for moral judgment in war. Key works include ‘War and International Justice’ (2001) and ‘The Morality of War’; strong on jus post bellum and international justice.
• *Jeff McMahan (leading revisionist)*: **‘Killing in War’ (2009) and related works challenge traditional symmetry. Argues that unjust warriors lack full moral permission to kill; emphasizes individual responsibility and dependence of in bello on ad bellum.
• Other revisionists: David Rodin, Cécile Fabre, Seth Lazar, Henry Shue (focus on rights-based critiques, liability, and individual ethics).
• Earlier 20th-century contributors: Elizabeth Anscombe (“War and Murder”), Thomas Nagel (“War and Massacre”), Paul Ramsey, James Turner Johnson (historical/theological modernizers).

In summary, modern JWT provides practical, principled tools to restrain war’s brutality while acknowledging it can sometimes be a lesser evil. It remains influential (and contested) in debates over drones, cyberwar, AI weapons, terrorism, and interventions. Traditionalists align more closely with existing laws of war; revisionists push for deeper individual moral accountability. Both schools converge on protecting non-combatants and proportionality.

Comparison of Classical and Modern JWT

Classical Just War Theory refers to the historical development of the tradition, primarily from its Christian theological roots in late antiquity through the medieval and early modern periods. It was systematized as a moral and theological framework for evaluating war within a Christian (and later natural-law) context.

Key figures include St. Augustine (4th–5th century CE), who first clearly articulated Christian justifications for war as a regrettable necessity to restore peace and punish wrongdoing, and St. Thomas Aquinas (13th century), who formalized the core criteria in his Summa Theologica. Later contributors like Francisco de Vitoria, Francisco Suárez, Hugo Grotius, Samuel Pufendorf, and Emerich de Vattel expanded and secularized it somewhat, universalizing it beyond Christendom (e.g., applying it to European encounters with indigenous peoples) and laying groundwork for international law.

Modern Just War Theory marks a 20th-century revival and philosophical reorientation, driven by the horrors of world wars, nuclear weapons, Vietnam, and later conflicts (e.g., post-9/11 terrorism, humanitarian crises). It shifted from primarily theological/natural-law foundations to secular, rights-based philosophical analysis, often aligned with international humanitarian law (IHL), human rights, and analytic ethics.

Michael Walzer’s ‘Just and Unjust Wars’ (1977) is the seminal modern text, reviving the tradition in a secular, liberal framework. Subsequent thinkers include Brian Orend (emphasizing jus post bellum), and a major internal debate between traditionalists/orthodox (Walzer-influenced, defending state-centric and legal paradigms) and revisionists (e.g., Jeff McMahan, Cécile Fabre, Seth Lazar), who challenge core orthodox assumptions with more individualist, liability-focused views.

Key Similarities Classical vs Modern JWT

Both share the same basic tripartite structure (though jus post bellum is far more developed in modern versions) and core criteria aimed at restraining war’s brutality while allowing it as a lesser evil:

• Jus ad bellum (justice of resorting to war): Just cause, legitimate authority, right intention, last resort, reasonable prospect of success, proportionality.
• Jus in bello (justice in conduct): Discrimination/non-combatant immunity, proportionality of means, military necessity.
• Goal: War must serve justice/peace, not vengeance or conquest; non-combatants protected; force minimized.

The tradition as a whole rejects both pacifism (war never justified) and realism (no moral limits on war).

Key Differences Classical vs Modern JWT

Core tensions in the comparison

• Traditional JWT was more collectivist and state/sovereignty-focused (pre-modern nation-state system). Modern versions grapple with individualism (revisionists reduce war to individual rights/liability) vs. collectivism (traditionalists preserve state rights and combatant equality for practical/legal reasons).
• Traditional was often more permissive of certain offensive/punitive wars; modern is more restrictive due to Westphalian/UN norms but expansive on humanitarian grounds.
• Modern JWT is far more debated internally (traditionalist vs. revisionist divide dominates contemporary philosophy, military academies, and IR) while classical was more unified under theology.

In summary, traditional JWT provided the enduring moral skeleton rooted in faith and natural law, while modern JWT secularized, philosophically refined, and legally operationalized it, making it more applicable (and contested) in a globalized, rights-conscious world. Both remain influential in ethics, policy, and law, though critics argue modern warfare (e.g., cyber, drones, hybrid conflicts) strains the framework.

Pacifism & Revisionist critiques in Just War Theory

Revisionist critiques in Just War Theory (JWT) refer to a major philosophical movement in modern JWT that challenges the foundational assumptions of the orthodox or traditionalist view, most prominently associated with Michael Walzer’s ‘Just and Unjust Wars’ (1977). Led primarily by Jeff McMahan (in works like ‘Killing in War’, 2009, and earlier essays from 1994 onward), and joined by thinkers such as David Rodin, Cécile Fabre, Helen Frowe, Lionel McPherson, and others, revisionists argue that traditional JWT rests on flawed moral foundations. They seek a more consistent, individual-rights-based ethics of war that aligns better with ordinary principles of self-defense, responsibility, and liability outside of war.

Revisionism is often called “reductivist” or “individualist” because it reduces the morality of war to the aggregation of individual moral permissions and liabilities (e.g., defensive harm), rather than treating war as a special, collective, or state-centric domain with its own rules. It rejects the idea that international law or pragmatic military conventions should define the “deep morality” of war.

Key Implications of Revisionist Critiques

• Individual moral accountability: Soldiers must assess the justice of their war and often refuse unjust ones (conscientious objection encouraged).
• Expanded humanitarian intervention: Revisionists are more permissive of interventions to stop atrocities.
• Rejection of state sovereignty as absolute: National defense is limited; wars of aggression or even some defensive wars may be unjust.
• Alignment with individual self-defense ethics: War is not morally exceptional.

Pacifist views represent a spectrum of positions that fundamentally challenge Just War Theory by rejecting or severely restricting the moral permissibility of war and organized violence. While JWT occupies a middle ground, acknowledging war’s horrors but permitting it as a lesser evil under strict criteria, pacifism insists that war is either intrinsically immoral or practically impossible to justify in real-world conditions.

Key pacifist proponents include Leo Tolstoy, Mahatma Gandhi, Martin Luther King Jr. (absolute/non-violent resistance), and modern philosophers like Andrew Fiala, Robert L. Holmes, and Cheyney Ryan. Contingent pacifism has been philosophically developed by Larry May (explicitly from a JWT framework) and implicitly supported by some revisionists (e.g., David Rodin’s skepticism of state self-defense rights).

Key Implications of Pacifism Critiques

• JWT’s critique of pacifism: Absolute pacifism is “dangerously otherworldly”, it fails to protect innocents from aggression (e.g., no response to genocide or invasion) and ignores human sinfulness/imperfection. Contingent pacifism is seen as overly pessimistic about real-world application of criteria.
• Pacifist critique of JWT: It provides a “smokescreen” or illusion of moral control, enabling more wars by legitimizing violence rather than abolishing it. Even “just” wars escalate, cause unintended harms, and rarely satisfy all criteria perfectly. Revisionism, while stricter, still concedes too much ground to violence.
• Revisionism’s bridge: By rejecting combatant equality and demanding high individual responsibility, revisionists expose JWT’s internal tensions. This has led some (including May) to advocate contingent pacifism from within the tradition: modern wars’ scale, uncertainty, and collateral damage make them impermissible in practice.

In essence, classic JWT stands farthest from pacifism (as a permissive framework), while revisionist JWT narrows the gap significantly, sometimes collapsing into contingent pacifism. Absolute pacifism remains the starkest antithesis, viewing any JWT-style justification as morally corrupting. Contemporary debates (especially post-Vietnam, Iraq, and amid drone/AI warfare) often blur these lines, with many ethicists seeing “functional pacifism” in international practice and calls for “just peace” alternatives that transcend both traditions.

The choice ultimately turns on whether one believes moral rules can (and should) ever license collective lethal force, or whether non-violence remains the only consistent path to true justice and peace.

American Essay. Published April 15, 2026. ©All Rights Reserved