Although the Indian epic, the Mahabharata, offers the first written discussions on ‘just war’, the first notable advancements were made by Augustine of Hippo, who established that Christians should be pacifists philosophically, but that defence, were it necessary to the long-term preservation of peace, should be employed.
Centuries later, Tommaso d’Aquino (known conventionally as Thomas Aquinas) expanded upon St. Augustine’s original arguments to define the conditions under which war could be just. He lays these out in his Summa Theologica:
- War must occur for purposes other than the pursuit of wealth or power — ‘good and just’ purposes.
- War must be waged by a ‘properly instituted authority’ — the state.
- War must have peace as its central motive, even in the midst of violence.
Later, the Escuela de Salamanca expanded Aquinas’ understanding of just war. In their vein of thought, war was established as one of the worst evils suffered by mankind. Hence, war could only be waged were it to prevent a greater evil. Just war is now expanded to:
- War waged in self-defence. However, if failure is the greater probability, it is a waste of human life and therefore not just.
- War waged preventively against a tyrant who plans to attack.
- War waged in order to punish a guilty enemy — guilty populaces as well as restoring land and wealth are included here.
In addition, the Escuela concluded that war cannot be legitimised or the contrary on the mere basis of its original motivation. Thus, they establish a set of additional requirements:
- The military response must correspond to the magnitude of the evil — additional violence is unjust.
- If a war is popularly opposed, it is illegitimate — the governing authorities’ declaration of war is not sufficient to justify it.
- Moral limits remain existent once the war has begun — no killing of hostages or innocents.
- The two parties must exhaust all diplomatic approaches to the problem — war is to be used only as a last recourse.
It thus becomes apparent that just war is only possible in the complete absence of the belligerence of human nature and in the neglecting of all conventional motivations and principles of war; not to mention its fundamental requirement of the unattainable degree of objectivity necessary to determine these factors in absolute terms.