Civics · Law · Geopolitics: The Rules of War and Peace

Facing war, there are three stances: realism says war has nothing to do with morality, only interest; pacifism says all war should be banned; just war theory takes the middle road — war is sometimes unavoidable, but must be morally constrained. In the West this tradition is often traced to Augustine and systematized by the medieval theologian Thomas Aquinas. Its core design is to split "the rightness of war" into two mutually independent questions:

• Justice of going to war (jus ad bellum): when one has the right to fight. Classic thresholds — just cause (e.g. resisting aggression), legitimate authority, right intention, last resort (peaceful means exhausted), reasonable prospect of success, and proportionality (the evil of war not exceeding the evil it prevents).
• Justice in war (jus in bello): how one must fight once it starts. Two iron rules — distinction (strike only combatants, never target civilians) and proportionality (collateral harm must not exceed the military gain).

The most elegant point is that the two are independent: a war with a just cause can still be fought by unjust means (e.g. massacring civilians); a war with no just cause still binds its soldiers to the rules of combat. It's like splitting "do you have permission to launch" and "runtime behavior constraints" into two checks — permission granted, an out-of-bounds action at runtime is still a violation.

• From theology to law: many of its intuitions were later written into modern law — the UN Charter narrows "lawful war" to just two grounds, self-defense and Security Council authorization, mapping onto "just cause + legitimate authority."
• The threshold dilemma: what counts as "peaceful means exhausted" always leaves room for interpretation; and "reasonable prospect of success" means a weak party's just resistance may be judged "shouldn't fight" simply because it can't win — the threshold is not symmetric between strong and weak. The tradition is more open to imminent preemption than to preventive war against a distant threat.

The "constraint beats nothing" logic: since war can't be eliminated, rather than let "the victor is right" reign, better to set a standard — imperfect as it is — that puts the burden of justification on those who start a war and lets atrocities be condemned. The "moral packaging" logic: critics worry the theory instead hands war a moral vocabulary — every side can call its own war "just," turning the theory into rhetoric for going to war rather than a brake on it. The two sacrifice opposite things: one may become a license to fight, while pure pacifism may stand by helpless in the face of aggression.

"Just war theory is just a defense of war" — quite the opposite. Its default is that war needs justifying: the burden of proof lies on the party going to war, and failing the thresholds makes it unjust. It doesn't judge "who is the good guy," only "is this war, this way of fighting, up to standard" — a "good" regime can equally fight an unjust war.

If just war theory governs "whether to fight," international humanitarian law (IHL, also the law of armed conflict) governs "what you may not touch once fighting starts." Its origin is concrete: after the 1859 Battle of Solferino, the Swiss Henry Dunant, appalled by wounded soldiers left untended, drove the founding of the International Committee of the Red Cross and the first Geneva Convention of 1864. Today's core is the four Geneva Conventions of 1949 (protecting wounded soldiers on land, the wounded and shipwrecked at sea, prisoners of war, and civilians) plus the two Additional Protocols of 1977. Its design philosophy is a balance between "military necessity" and "humanity": accept that war is to be won, but keep a floor for "those no longer, or not, taking part." Two pillars — distinction (combatants vs civilians) and proportionality (collateral harm not exceeding military gain); most of these rules are already customary international law, binding all parties whether or not they signed.

• Two bodies of law, divided labor: "Hague law" (the 1899 and 1907 Hague Conventions) governs the means and methods of warfare (what weapons, how to fight); "Geneva law" governs what to do with people (wounded, POWs, civilians).
• Common Article 3: shared by all four Conventions, it extends a minimum humane floor (no ill-treatment, no summary execution) to non-international armed conflict (e.g. civil war) — filling the huge gap of "civil war beyond international law's reach." The 1977 Protocols extended this further, yet not all major powers have ratified them all in full: the more a rule limits the strong's freedom to fight, the harder it is to win universal acceptance.

The "hold the floor" logic: even in the extreme state of war there must be red lines that can never be crossed (no massacring POWs, no targeting civilians), or violence spirals out of control and postwar reconciliation becomes impossible. The "rules tie our hands" logic: critics worry overly strict rules penalize the law-abiding side — especially when the adversary wears no uniform and blends into civilians, "distinction" can be exploited as a shield.

"The laws of war ban all civilian casualties" — inaccurate. IHL does not require "zero civilian casualties"; it bans "targeting civilians" and "collateral harm disproportionate to the military gain." Civilian casualties from a lawful strike on a military objective, weighed for proportionality, do not necessarily constitute a war crime — which is exactly where proportionality is hardest to judge and most contested.

Nuclear weapons push war to a paradoxical extreme: a weapon too powerful to use. The strategist Bernard Brodie put it in 1946: the chief purpose of a military has been to win wars; from now on it will mainly be to avert them. From this grew the logic of deterrence: not by "winning," but by making an opponent certain that "striking first carries an unbearable cost." In the Cold War it crystallized into Mutually Assured Destruction (MAD): both sides hold a "second-strike capability" — even after absorbing a first nuclear blow, enough force survives to retaliate devastatingly. So striking first equals suicide — like a mutual-destruction interlock. Stabilizing this logic depends, counterintuitively, on making your own retaliation "un-killable" (e.g. submarine-launched forces), not on being able to "defend against it."

• The non-proliferation bargain: the 1968 Treaty on the Non-Proliferation of Nuclear Weapons (NPT) tried to freeze the nuclear club — non-nuclear states pledge not to develop weapons, nuclear states pledge to pursue disarmament and share civilian nuclear technology; the execution of this "non-proliferation for disarmament" bargain remains contested to this day.
• Clash with just war theory: nuclear deterrence directly conflicts with "distinction" — threatening to destroy cities (i.e. civilians) violates "don't target civilians." So one school argues for shifting to a "counterforce" strategy aimed only at military targets — but that in turn may make nuclear war look "winnable" and lower the threshold.

The "peace of terror" logic: since nuclear weapons appeared, great powers have not fought a direct all-out war; deterrence may have bought "stability" with "terror" — a cost so unimaginable that rational actors are forced to restrain themselves. The "peace on a cliff-edge" logic: this stability rests on fragile assumptions — the opponent must be rational, information not misread, systems not malfunction, and it must not fall into irrational or non-state hands; a single misjudgment could be irreversible, and it holds all of humanity hostage. The two sacrifice opposite things: relying on deterrence stakes everything on a catastrophic tail risk, while full abolition faces the problem of verifying that no one is secretly building.

"More nukes means more safety" — not quite. The key to deterrence isn't quantity but the credibility of a "second-strike capability": as long as the opponent is certain you can retaliate devastatingly after being hit, deterrence holds; stockpiling beyond that instead raises the risk of misjudgment and accident.

The first three blocks all "make rules"; this one faces an honest question: once written down, why would rules be obeyed? Domestic law is backed by police, courts, and prisons — an enforcement machine; international society has no enforcer standing above states. The laws of war therefore lean on weaker mechanisms: reciprocity (I treat your POWs well so you treat mine well), reputation, and after-the-fact accountability. After WWII the Nuremberg trials established that "individuals are responsible for war crimes and cannot escape by pleading 'following orders'"; later came standing institutions like the International Criminal Court (ICC). But this enforcement system looks more like "retrospective, selective, dependent on great-power cooperation" accountability than the immediate, universal compulsion of domestic law.

• The "victor's justice" doubt: Nuremberg set a precedent for accountability, but the judges were the victors, trying only the losers' crimes — seen by some as "justice finally done," criticized by others as selective accountability; stated here, not judged.
• The jurisdiction gap: the ICC's jurisdiction depends on state consent, and several major powers still have not joined or do not recognize it — those most capable of waging war are often least bound by it. The rules were designed for state-vs-state war and often strain against new conflicts such as those involving non-state armed groups.

The "weak rules beat no rules" logic: even poorly enforced, the laws of war changed the discourse and the threshold — giving atrocity a name (war crime), attaching stigma to violators, and giving victims a frame of reference to appeal to. To scrap them is to give up even the language of criticism. The "rules are an illusion" logic: realists hold that rules without enforcement are hollow before a state's survival interest; great powers breach them at will, and the rules become the weak's self-consolation or even the strong's propaganda tool — overrating them misjudges their force, while wholly denying them may tear down the only, fragile constraint there is.

"No one enforces the laws of war, so they're meaningless" — mistaking "weak force" for "zero effect." Militaries' rules-of-engagement manuals, the widespread (if imperfect) decent treatment of POWs, and the broad taboo on chemical weapons all show the rules did change the default of behavior. They can't stop every violation, but they raise its cost — which is quite different from "meaningless."