What is Just War Theory?
From both a historical and moral perspective, there is a strong presumption against the use of violence and aggression. Just war theory deals with the justification for overriding this strong presumption and waging war. Historically, the just war tradition represents the effort of Western cultures to regulate and restrain violence by establishing widely recognized rules of combat. The theoretical aspect of just war theory, on the other hand, is concerned with ethically justifying war. Moral justification for war has its roots in Christian theology and the writings of St. Thomas Aquinas. Together, traditional rules of combat and moral ideals have helped to form the rules of warfare found in international law. The set of guidelines commonly known as the "war convention" is made up of these moral norms and legal precepts.
Theorists distinguish between the rules of jus ad bellum and jus in bello. The rules of jus ad bellum pertain to the circumstances under which states can acceptably wage war, while the rules of jus in bello serve as guidelines for fighting fairly once war has begun.
Formulated in international law and recognized by most cultures, the rules of jus ad bellum serve as principles to determine when war and the use of violence are justifiable. Only when the criteria of jus ad bellum are met can the use of violent force be permitted.
Having just cause is often thought to be the most important condition of just war. Many hold that the only just cause for war is self-defense against aggression. In 1974, the United Nations General Assembly defined aggression as "the use of armed force by a State against the sovereignty, territorial integrity or political independence of another State." States' rights to territorial integrity and political sovereignty are derived from the rights of individuals to build a common life and rest on the consent of their members. Insofar as a state protects the lives and interests of individuals, it cannot be challenged in the name of life and liberty by any other state. International law holds that a state engaging in war, other than for purposes of self-defense, commits the crime of aggressive war.
However, many have noted that this conception of just cause is far too narrow. First, it is commonly thought that states can defend themselves against violence that is imminent, but not actual. When the threat is clear and the danger close, military acts of "anticipation" are often considered morally justified. For example, many believe that states are justified in conducting pre-emptive strikes in cases where there is a sufficient threat, and failure to exercise military force "would seriously risk their territorial integrity or political independence." There are threats with which no nation can be expected to live.
In addition, many have noted that the "aggressor-defender" dichotomy is an oversimplification. Intervention across national boundaries can sometimes be justified, and the legal existence of a regime does not guarantee its moral legitimacy. They believe that force may sometimes be used to correct grave public evils or to address massive human rights violations. When a government turns savagely upon its own people, it violates their human rights and imposes conditions to which they could not possibly consent. Such a government lacks moral legitimacy, and its political sovereignty and rights to govern are called into doubt. Because governments that engage in massacre are criminal governments, wars of interventions resemble law enforcement or police work.
The Principles of Jus Ad Bellum
The other principles central to jus ad bellum are right authority, right intention, reasonable hope, proportionality, and last resort.
The principle of right authority suggests that a war is just only if waged by a legitimate authority. Such authority is rooted in the notion of state sovereignty and derived from popular consent. Even if their cause is just, individuals or groups whose authority is not sanctioned by society members cannot justifiably initiate war. It is important to note, however, that corrupt governments that rule arbitrarily and unjustly may not warrant the allegiance of the populace. In these cases, state sovereignty disintegrates, and individuals may have a right to declare war in order to defend themselves from an illegitimate government. Struggles for independence by distinct communities that are ready and able to determine the conditions of their own existence may sometimes be justified.
According to the principle of right intention, the aim of war must not be to pursue narrowly defined national interests, but rather to re-establish a just peace. This state of peace should be preferable to the conditions that would have prevailed had the war not occurred. Right intention is tied to the conditions of jus in bello, (justice in war) and forbids acts of vengeance and indiscriminate violence. Because the proper object of wars is a better state of peace, just wars are limited wars. Unconditional surrender is often thought to violate the principle of right intention because it deprives a nation of its rights and sovereignty, and in effect destroys it. Nevertheless, in cases such as Nazism, where a government regime poses a threat to the very existence of entire peoples, the conquest and reconstruction of an enemy state may be a legitimate military goal.
Here, however, it is important to note that securing peace often overlaps with the protection of self-interest. For example, if the only way to secure peace is to annex a belligerent neighbor's territory, proper intention is linked to pursuing self-interest. Other proper intentions for war, such as defending an oppressed group and securing its freedom, may be abandoned because such a war is deemed too costly.
In addition, just wars must have a reasonable chance of success. According to the principle of reasonable hope, there must be good grounds for believing that the desired outcome can be achieved. Arms may not be used and deaths incurred in a futile cause or when the probability of success is very low. This principle involves weighing the costs and benefits of waging war, and "emphasizes that human life and economic resources should not be wasted" on war efforts that are certain to fail. However, some note that in some cases it is necessary as a matter of moral principle to stand up to bullying forces even if there is little chance of success. For the sake of national pride, fights that are seemingly hopeless may sometimes be justifiably undertaken.
The principle of proportionality stipulates that the violence used in the war must be proportional to the attack suffered. The means should be commensurate with the ends, as well as be in line with the magnitude of the initial provocation. States are prohibited from using force not necessary to attain the limited objective of addressing the injury suffered. For example, if one nation invades and seizes the land of another nation, this second nation has just cause for a counter-attack in order to retrieve its land. However, if this second nation invades the first, reclaims its territory, and then also annexes the first nation, such military action is disproportional. In addition, the minimum amount of force necessary to achieve one's objectives should be used. Thus, the principle of proportionality overlaps with jus in bello, the conditions for how war should be fought.
Finally, the principle of last resort stipulates that all non-violent options must be exhausted before the use of force can be justified. A just war can only be waged once all other diplomatic avenues have been pursued.
 James Turner Johnson, Just War Tradition and the Restraint of War: A Moral and Historical Inquiry. (New Jersey: Princeton University Press, 1981), 4. <http://books.google.com/books?id=6aCSQgAACAAJ>.
 Alex Moseley," Just War Theory," in The Internet Encyclopedia of Philosophy (2009, accessed February 3, 2003). <http://www.utm.edu/research/iep/j/justwar.htm>.
 Michael Walzer, Just and Unjust Wars: A Moral Argument with Historical Illustrations, 2nd Edition. (New York: Basic Books, 1997), 44. 4th Edition (2006) available here.
 Leslie C. Green, The Contemporary Law of Armed Conflict. (Juris Publishing, 2008). <http://www.amazon.com/The-Contemporary-Armed-Conflict-International/dp/1578232422>.
 Ibid., 59.
 Walzer, op. cit 54.
 Walzer, op. cit 85.
 Johnson, op. cit 328.
 David Luban, "Just War and Human Rights" Philosophy and Public Affairs, Vol. 9, No. 2. (Winter, 1980, accessed on February 3, 2003), 160-181. <http://www.jstor.org/stable/2265110>.
 Walzer, op. cit 107
 Don Hubert and Thomas G. Weiss et al. The Responsibility to Protect: Supplementary Volume to the Report of the International Commission on Intervention and State Sovereignty. (Canada: International Development Research Centre, 2001), 139. <http://books.google.com/books?id=31qFeSkSb5IC>.
 Walzer, op. cit 93.
 Walzer, op. cit 121.
 Walzer, op. cit 114.
 Hubert and Weiss, et al., 139.
 Hubert and Weiss, et al., 139
Use the following to cite this article:
Maiese, Michelle. "Jus ad Bellum." Beyond Intractability. Eds. Guy Burgess and Heidi Burgess. Conflict Information Consortium, University of Colorado, Boulder. Posted: June 2003 <http://www.beyondintractability.org/essay/jus-ad-bellum>.