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Jus Ad Bellum and Jus In Bello in International Humanitarian Law

by Sharmishtha Sharma
Jus Ad Bellum and Jus In Bello in International Humanitarian Law
Laws of war - Jus ad Bellum and Jus in Bello

What do these two terms talk about?

Right to engage in warRight conduct in war
For what reason?In what means?
To what end?In what ways?

Jus ad bellum

It refers to “legitimate reasons a State may engage in war”. These rules focus on certain criteria for what makes a war just. The prohibition against the use of force amongst States and the exceptions to it (self-defense and UN authorization for the use of force), set out in the United Nations Charter of 1945, are the core ingredients of Jus ad Bellum.

Article 51 of the UN Charter clarifies: “Nothing in the present Charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs against a Member of the United Nations”.

  1. Proper Authority: 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. Proper authority is what differentiates war from murder. Therefore, a soldier is treated as a prisoner of war (POW) and not a criminal because they are operating under the proper authority of the State and cannot be held individually responsible for actions committed under the orders of their military leadership. 
  • Just Cause/Right Intention: According to the principle of right intention, the aim of war must not be to pursue narrowly defined national interest, 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. Wars cannot be fought simply to annex property or install a regime change. Right cause includes humanitarian intervention, particularly when actios “shock that conscience”. The responsibility to protect covers more in depth the nature of humanitarian intervention.
  • Probability of Success: According to this principle, there must be good grounds for concluding that aims of the just war are achievable. This principle emphasizes that mass violence must not be undertaken if it is unlikely to secure the just cause. However, wars are fought with imperfect knowledge, so one must simply be able to make a logical case that one can win.
    These criteria move that conversation from moral and theoretical grounds to practical grounds. Essentially, this is meant to gather coalition building and win approval of other state actors.
  • Proportionality: The principle of proportionality stipulates that the violence used in the war must be proportional to the military objectives. The level of military victory must be proportional to the level of destruction that ensues. However, if there is a high value military target in an area with far fewer civilians (a car or a private home) an attack and the collateral damage may be considered justifiable under the rule of proportionality.
  • Last Resort: The principle of last resort stipulates that all non-violent options must first be exhausted before the use of force can be justified. Diplomatic options, sanctions, and other non-military methods must be attempted or validly ruled out before the engagement of hostilities.

Jus in bello

It is a branch of international law which seeks to limit the effects of armed conflict by protecting persons who are not participating in hostilities, and by restricting and regulating the means and methods of warfare available to combatants. Jus in Bello includes two principles of discrimination and proportionality defines how much force could be used.

  • Principle of Distinction: The principle of distinction protects civilian population and civilian objects from the effects of military operations. It requires parties to an armed conflict to distinguish at all times, and under all circumstances, between combatants and military objectives on the one hand, and civilians and civilian objects on the other; and only to target the former. It also provides that civilians lose such protection should they take a direct part in hostilities.
  • Principle of Proportionality: Necessity and proportionality are established principles in humanitarian law. Under IHL, a belligerent may apply only the amount and kind of force necessary to defeat the enemy. Further, attacks on military objects must not cause loss of civilian life.
  • Principle of Humane Treatment: The principle of humane treatment requires that civilians be treated humanely at all times. Civilians are entitled to respect for their physical and mental integrity, their honor, family rights, religious convictions and practices, and their manners and customs. This principle of humane treatment has been affirmed by the ICRC as a norm of customary international law, applicable in both international and non-international armed conflicts.
  • Principle of Non-Discrimination: The principle of non-discrimination is a core principle of IHL. Adverse distinction based on race, sex, nationality, religious belief or political opinion is prohibited in the treatment of prisoners of war, civiloans, and persons hors de combat. All protected persons shall be treated with the same consideration by parties to the conflict, without distinction based on race, religion, sex or political opinion. Each and every person affected by armed conflict is entitled to his fundamental rights and guarantees, without discrimination. The prohibition against adverse distinction is also considered by the ICRC to form part of customary international law in international and non-international armed conflict.


The International Humanitarian Law (IHL) is inspired by considerations of humanity and the mitigation of human suffering. It comprises a set of rules, established by treaty or custom, that seeks to protect persons and property/objects that are, or may be, affected by armed conflict and limits the rights of parties to  a  conflict  to use methods and means of warfare of their choice. It is designed to balance humanitarian concerns and military necessity. Serious violations of international humanitarian law are called war crimes.

International Humanitarian Law applies to the belligerent parties irrespective of the reasons for the conflict or the justness of the causes for which they are fighting. If it were otherwise, implementing the law would be impossible, since every party would claim to be a victim of aggression. Moreover, IHL is intended to protect victims of armed conflicts regardless of party affiliation. That is why Jus in Bello must remain independent of Jus ad Bellum.

Further Readings:

  1. https://www.icrc.org/en/document/what-are-jus-ad-bellum-and-jus-bello-0
  2. https://www.icrc.org/en/war-and-law/ihl-other-legal-regmies/jus-in-bello-jus-ad-bellum
  3. https://www.icrc.org/en/document/jus-ad-bellum-jus-in-bello
  4. https://international-review.icrc.org/articles/can-jus-ad-bellum-override-jus-bello-reaffirming-separation-two-bodies-law

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