Are there universal criteria for Just War?

Yes, there are universal criteria for Just War, often referred to as the Just War Theory.

The Just War Theory is a doctrine that seeks to ensure war is morally justifiable through a series of criteria, all of which must be met for a war to be considered just. The criteria are split into two groups: 'jus ad bellum' (the right to go to war) and 'jus in bello' (right conduct within war).

The 'jus ad bellum' criteria include: Just Cause, where war is only permissible to confront a real and certain danger; Comparative Justice, where the injustice suffered by one party must significantly outweigh that suffered by the other; Legitimate Authority, where only duly constituted public authorities may wage war; Right Intention, where force may be used only in a truly just cause and solely for that purpose; Probability of Success, where arms may not be used in a futile cause or in a case where disproportionate measures are required to achieve success; and Last Resort, where force may be used only after all peaceful alternatives have been seriously tried and exhausted.

The 'jus in bello' criteria include: Proportionality, where the use of force must be proportional to the harm suffered; and Discrimination, where armed forces must distinguish between combatants and non-combatants, with non-combatants being immune from attack.

These criteria are not universally accepted, and their interpretation can vary. For example, what constitutes a 'just cause' or 'right intention' can be subjective and open to interpretation. Furthermore, the Just War Theory does not account for wars of aggression or pre-emptive strikes, which some argue can be just under certain circumstances.

Despite these limitations, the Just War Theory provides a framework for evaluating the morality of war. It is used by politicians, military leaders, and scholars to analyse the ethical dimensions of conflict and to guide decisions about when and how to engage in war.