Jus ad Bellum is a concept that informs the reasons behind why a military intervention is carried out from an ethical perspective. Hence, instead of a merely “realist” (in the sense this word generally carries in political science) reason behind the conduct of war, such as the preservation of self-interest, jus ad bellum refers to a concept of war that contains a clear ethical concept of justice, such that the logic for why military operations are conducted follow from the ethical concept at stake.
Certainly, self-interest could also perhaps be called a form of jus ad bellum, in so far as one suggests that the most just act one may take is to preserve one’s own interests. However, this is a very relativistic and almost emotivist concept of justice, wherein justice would clearly be merely the preference of one party over another. Jus ad bellum by definition implies a clear ethical reason for why a conflict is correct, and the concept of justice at stake in the definition has to be sincerely felt by those participating in the conflict. Morale emerges in those soldiers who feel not only a unity of purpose, but also a justice to their purpose.
It can also be said that the concept of jus ad bellum always contains an element of relativism: the very reason why wars are fought is because there is a disagreement between two parties. However, this does not discount the moral realism of jus ad bellum. For one side of the struggle could merely reject such a concept, for example, pursuing their own self-interests, whereas the opposing side may appeal to a concept of justice. Whereas “every military society throughout history has had a distinct ethos”, jus ad bellum in this sense would be such an ethos, providing the logical supplement to the community of the esprit de corps. In so far as “honorable service requires a rock-solid ethical base to uphold the highest standards of conduct, especially in the difficult and morally trying conditions of combat”, jus ad bellum provides such an inexorable foundation, preventing fragmentation of the unity of purpose.
 »Our Army Profession«, p. 10.
 Ibid., p. 11.