Just War Theory

by Nile Stanton
Thursday - March 23, 2023

      Just war theory provides a set of guidelines that can help political and military leaders to make ethical and responsible decisions. The guidelines can help ensure that nations act in ways that are consistent with their values and that they are held accountable for their actions. They can help promote accountability and transparency in military actions and help create a more peaceful and just world. Therefore, since only a small percentage of people know anything about just war theory at all, I encourage more to learn about it. Here is your opportunity.

      For hundreds of years, the morality and legitimacy of wars have been evaluated under what is called just war theory. This theory can be logically accepted as a decisional paradigm if, and only if, one first accepts as a priori the justifiability of war at least under a particular set of circumstances. While some people vigorously contend that war, due to its very nature, can never be moral under any circumstances, that matter exceeds the scope of this essay.

      James Turner Johnson of Rutgers University has observed that,

Just war is an historical tradition formed by experience and reflection, including much that is neither specifically theological (or even religious), nor philosophical. It has been strongly influenced by international law, the traditions of chivalry, and soldierly practices derived from the experience of many battles.
Nevertheless, I suggest that it is clear beyond cavil that it has been Christian (primarily Catholic) scholars, especially St. Augustine (354-430 A.D.) and St. Thomas Aquinas (1224-1274), whose writings have had the most influence on the formulation of the elementary core of just war theory. Most scholarly discussions about "just war" hark back to his Question 40, Article 1, "On War," of Part II of the Second Part of the Summa Theologica.

      The long-term impact of St. Thomas Aquinas' remarks in addressing Question 40 cannot be underestimated. I submit that those remarks profoundly influenced just war theory and especially its acceptability.  His comments in "Of Hatred," which addresses Question 29 of Part I of the Second Part, and observations made in addressing Questions 69, 100, and 104 are generally ignored in "just war" discussions even though relevant at a theoretical level. In my view, those passages tend to be inconsistent with the implications of his pronouncements in famed Question 40.  

      Emendations to the general theory of just war have been based upon the secular writings of Marcus Tullius Cicero (106-43 B.C.), Hugo Grotius (1583-1645), and others. Too, the writings of Charles Louis de Secondat, better known as Baron de Montesquieu (1689-1755), in The Spirit of Laws (specifically Chapter 2 titled "Of War" in Book X, "Of Laws in the Relation They Bear to Offensive Force") as well various writings of John Locke have also contributed to the theory.

      In more recent years, positive law set forth in the various Hague and Geneva Conventions, the Nuremberg Charter, the United Nations Charter, and a variety of other such generally accepted enunciations of collectively developed standards have also informed just war theory. The most recent positive law relating to duties and rights of combatants and civilians during war is the 1977 Protocol Additional to the Geneva Conventions of 12 August 1949.

      Evolving just war theory and the law of armed conflict attempt to take into account and harmonize various moral values reflected in books and essays of many people who have devoted considerable thought to this subject, as well as war experience and tradition. Just war theory and the law of armed conflict are premised on the international norms set forth in positive law and have a continuing impact on those norms.

      Here are the main features of current just war theory.

      Just war theory involves the analysis of (A) jus ad bellum, when it is just to participate in war and (B) jus in bello, what is just in the conduct of war. Military action is appropriate only if the established criteria of both are met in any given situation. 

      I. Jus Ad Bellum. -- It is held that states are morally and legally bound not to war against one another unless certain criteria are met. It is up to individual states (which at this level are conclusively presumed to reflect the collective will of their citizens) to determine before going to war that all these criteria have been met.
      It is assumed that states comprise people of goodwill who are generally unwilling to engage in the intentional infliction of deadly force against the citizens of another state unless truly justifiable to do so. Hence, all states' citizens (including those who also happen to be in the armed forces) have, I submit, a duty to attempt to assure that jus ad bellum criteria are met. After all, once war begins governments and their people are at risk of serious harm. 
      While there is not complete agreement on what the criteria of jus ad bellum are, the following components are commonly accepted:

    A.  Just Cause. -- The determination of just cause requires the balancing of some values but rarely involves invoking arcane theories of justice. Just cause requires that we not put trivial preferences, insults to national pride, and even some gross violations of the law of nations above the duty to preserve peace rather than go to war. Generally, the existence of the state or the lives of its citizens must be at stake. The "cause" would be "just" to engage another state in war if agents of that state (acting under color and scope of lawful authority) were to make a substantial attack of some sort that is deliberately designed to destroy or impair our state or significantly injure our citizenry. Indeed, self-defense is the only just cause for war that is formally recognized in modern international law. It is properly invoked to protect the integrity and fundamental nature of the state or the lives of its citizens when those are clearly threatened or attacked. This right of self-defense has often been construed to subsume the right to intervene in order to protect one's "neighbor" and the right to punish states that do wrong.

   B. Lawful Authority. -- Since war is an organized activity of a state, it is essential that war be undertaken only with the proper authority of the entity that is, under that state's own laws, granted the power to do so. This entity might a Queen or King, a President, or some other leader; or the entity might be some group. It depends upon the structure of the decision-making process in each state. In the United States of America, the lawful authority to commit the U.S. military to war vests solely and exclusively in the Congress. The President has the authority to decide how a war should be prosecuted once it begins and, by virtue of being the chief executive of the United States, has an implied duty to assure that the sovereignty of the state and the lives of citizens are protected. Article 1, Section 8, Clause 11 and Article 2, Section 2, of the Constitution, the War Powers Act of 1973, as well as custom, practice, and necessity, are weighed here. 

    C. Just Intent. -- This requires that the intent of going to war be to promote or secure peace, not merely to obtain revenge, wealth, or personal glory. Just intent is based on natural law and religious and secular values consistent with the Judeo-Christian ethic to "love thy neighbor." The goal must be to do good, not harm. The firm commitment of a state to abide by all just war criteria evinces an intention to do that which is just.

   D. Last Resort. -- This criterion and the one which follows (reasonable hope of success) are in a real sense subordinate to just intent. After all, if a state undertakes war except as a last resort its intentions are certainly suspect. All states are deemed duty-bound to avoid the consequences of war if it is reasonably possible to do so. Good faith efforts to avoid war must be actively pursued, viz. negotiations should be engaged in, compromises sought, economic sanctions applied, appeals to reason made, cooling off periods taken, and peace-promoting activities by appropriate international bodies utilized in efforts to redress grievances before resort to war is justified.

    E. Reasonable Hope of Success. -- A hopeless war is deemed pointless and contrary to common sense and justice. That does not mean, however, that a state and its citizenry need meekly submit to the murderous exercise of raw power.  An increase in public support from within and resources of allies might transform a hopeless undertaking into a reasonable one at some point. States are enjoined from going to war without reasonable hope of success because to do so would throw away the lives and resources of its citizens and risk destruction of the state.

      II. Jus In Bello. -- Right conduct during war is of singular importance to people in the armed forces. In my view, American armed forces have generally done a much better job of adhering to the spirit and requirements of jus in bello than states themselves have done in adhering to the spirit and requirements of jus ad bellum. (Many states tend to ignore their duties. The U.S. military normally honors its obligations.) One reason for this, I suggest, is that governments rarely, if at all, educate their citizens about prevailing just war theory or law of war conventions. On the other hand, Article 1 of Hague Convention IV of 1907 mandates that states "issue instructions to their armed forces which shall be in conformity with the regulations respecting the laws and customs of war on land." Other conventions have similar mandates. In accordance with such mandates, the U.S. has Department of Defense Directive No. 5100.77 (December 9, 1998), etc., and various specific service directives designed to guarantee training to assure that U.S. armed forces know their law of war obligations. These obligations are presented in various manuals, codes of conduct, and rules of engagement (ROE). All training manuals, codes of conduct, and ROE should, therefore, be in harmony with the two basic criteria of jus in bello.
    A.  Discrimination. -- Warring parties are obligated to discriminate between an enemy's armed forces and its civilian population. The principle of noncombatant immunity is largely premised on the notion that civilians not involved in supporting a state's war effort should not be harmed. It is often difficult to determine, however, which civilians are immune. Those civilians who are directly involved in the war effort (such as being part of the war-planning process or working to produce war materials) can be treated as combatants, others generally not. Civilians who engage in activities that are primarily designed to aid other civilians do not lose their immunity simply because the activities indirectly aid the enemy forces. Accordingly, a civilian dairy farm, for example, should not be attacked merely because a state's armed forces may drink some of the milk it produces.
    It is easy to see that the discrimination criteria of jus in bello can make targeting decisions problematic. It is much easier to determine when the armed forces of a warring state can be subjected to lethal force: at any time and any place they might be found so long as they have not surrendered, been captured, are injured, or are otherwise hors de combat.
    Civilians are not allowed to shield legitimate military targets and shed their immunity if they do so. However, under such circumstances, there is a duty to give those civilians warning and an opportunity to flee from the target area if it is reasonably possible to do so.
    "Military necessity" should not be used as a mere excuse or rationale to attack noncombatants. That precept should be invoked only under extraordinary circumstances. 

   B. Proportionality. -- The amount and type of force to be utilized in war should be the minimum necessary to end the war and secure peace. The good results which might be achieved through military action cannot be outweighed by the damage inflicted. For minimally desirable military ends, excessive destruction is not warranted. Undue collateral damage, whether attributable to lack of discrimination or lack of proportionality, might be construed to evince a murderous intent and should be assiduously avoided whenever possible.

      As international law has developed, the criteria of jus ad bellum have become increasingly restrictive, while the criteria of jus in bello, such as the prohibition of civilian targeting and the use of certain weapons, has become more comprehensive. This evolution of both has been essential in helping to ensure that wars are not as horrible as they could be and in promoting the maintenance of peace.


      My next essay, a relatively short one, will treat aggression and self-defense. Look for it here on Friday, the 31st.



* Nile Stanton lives in southern Spain. He was a professor for the University of Maryland University College for 20 years, where he taught U.S. active duty service members on U.S. military bases in Spain, Italy, Bosnia, and (mostly) Greece as well as online to troops throughout Europe and Asia. The course he taught most often (32 iterations) was the upper-level government course called “Law, Morality, and War.” Thereafter, he taught for the University of New England at its Tangier, Morocco, campus for two years, where his signature course was “War and Public Health.” He was born and raised a Quaker and tends to examine the excuses for war and lack of diplomacy more carefully and from a different perspective than many people.

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