Law of War and Just War Theory
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Law of War
Law of war: The law of war is international law and is based on the United Nations Charter and the various Geneva Conventions and their subsequent protocols. There is no reason to assume that the law of war coincides perfectly with the morality of war.
The law of war currently recognizes only two legal causes for going to war: (1) it is a defensive war against illegal attack that is in process or imminent, and (2) it is authorized by the United
Nations Security Council. Preventive war against future (non-imminent) illegal attack and humanitarian intervention (to protect citizens of the other country) are illegal.
The law of war currently holds that attacks are disproportionate (“indiscriminate”) just in case they are expected to cause incidental (i.e., unintended) harm to civilians or civilian objects that is
“excessive” in relation to the expected concrete military advantage.
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Just War Theory
Just war theory is a family of theories that developed out of the natural law tradition of moral theory (e.g., St. Thomas Aquinas (1225-1274), Francisco de Vitoria (1483-1546), Francisco
Suárez (1548-1617), Hugo Grotius (1583-1645), and Samuel Pufendorf (1632-92)). More recently it has been developed by Michael Walzer (1935-). Against pacificism, it holds that some wars are just. Against “realism” (roughly: state egoism) it holds that some wars are unjust. Much of the international law of war is based on just war theory.
Below, I interpret all principles as principles for moral permissibility , and not merely for justice
(wronging no one). Although they are typically formulated in terms of justice, I believe (1) authors often intend to address permissibility, and (2) they are most plausible when interpreted in terms of permissibility.
There are four kinds of principles (although the last two are of relatively recent origin):
Jus ad bellum (just war): These are the principles governing when going to war is permissible in principle.
Jus in bello (justice in war): These are the principles governing the permissibility in the conduct of war.
Jus ex bello (justice in terminating war): These are the principles governing when continuation of a war is permissible (and when termination is required).
Jus post bellum (justice after a war): These are the principles governing what is morally permitted after a war has been terminated (e.g., compensation, reform).
There are many variants of just war theory. Below I sketch a fairly standard view (focusing just on the first three traditional kinds of principles above):
Jus ad bellum: Going to war is permissible if and only if:
(1) There is a just cause . This is understood (1) almost always to include defensive war against an unjust attack (in process or imminent), (2) usually to include preventive war against

future unjust attack, and (3) sometimes to include humanitarian intervention (to stop a government from systematically and seriously violating, or from allowing such violation of, the rights of its citizens or residents).
(2) The war was declared by a competent authority (normally understood as the relevant official of a state).
(3) There is the right intention . This is typically understood as requiring that the intention in going to war includes (and perhaps be limited to?) the intention to pursue the just cause
(as opposed to merely taking advantage of the presence of the just cause to take revenge on the enemy).
(4) The war has a reasonable chance of success.
(5) Going to war is a last resort (alternatively: is necessary). This is typically understood as requiring that there be no less destructive (or harmful) way of achieving the relevant just cause goods
(6) The war is not expected to impose disproportionate harm relative to the just cause goods that it will achieve. Although this is not standard, this is best understood as follows.
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The war not impose narrowly disproportionate (and hence wrongful) harm without an overriding (lesser evil) justification (a wide proportionality justification ). o Here, all (relevant) harms to those who are not liable to such harm (who have not forfeited any of the protective force of their right against such harm; e.g., innocent non-combatants on a standard view) are narrowly disproportionate. o The relevant goods for the overriding justification are typically understood as including both just cause goods and bads (the just cause goods, and associated bads, specified in the just cause condition) and certain other good and bads. The other goods and bad may include everything that is good or bad for individuals
(e.g., economic goods and bads), or be restricted to certain just-cause-related goods and bads (e.g., disarming/incapacitating an aggressor, deterring future aggression, and preventing humanitarian crimes).

The war does not violate a greater-evil (impersonal) constraint (a wide proportionality constraint ; not a standard condition, but one that should be considered): The overall consequences of going to war are not so bad for individuals that it is impermissible, even if the war wrongs no one (by disproportionate or unnecessary harm).
Jus in bello: An attack in war is permissible if and only if:
(1) Discrimination: there is no intentional infliction of harm on non-combatants and nonmilitary targets
(2) Necessity: No less harmful action is at least as effective in achieving military goals.
(3) No narrowly disproportionate harm is imposed unless there is an overriding (lesser evil) justification in terms of wide proportionality (very large benefits of the relevant sort). See above for details.
(4) The war is not impersonally wrong because of very bad consequences (not a standard condition, but one that should be considered).
Jus post bellum (partial list):
(1) Punishment: It is permissible for the victors to subject wrongdoers (e.g., jus in bello war crimes) to punishment after a fair criminal trial.
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(2) Compensation: It is permissible for victors to extract compensation from wrongdoers for their victims (when compatible with the following principles).
(3) Reconstruction: It is obligatory for victors to assist in the reconstruction of the defeated countries.
(4) Respect of Sovereignty: It is obligatory for victors to respect the sovereignty of the defeated countries.
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