Just war theory deals with the justification of how and why wars are fought. The justification can be either theoretical or historical. The theoretical aspect is concerned with ethically justifying war and the forms that warfare may or may not take. The historical aspect, or the “just war tradition,” deals with the historical body of rules or agreements that have applied in various wars across the ages.
For instance, international agreements such as the Geneva and Hague conventions are historical rules aimed at limiting certain kinds of warfare which lawyers may refer to in prosecuting transgressors, but it is the role of ethics to examine these institutional agreements for their philosophical coherence as well as to inquire into whether aspects of the conventions ought to be changed.
The just war tradition may also consider the thoughts of various philosophers and lawyers through the ages and examine both their philosophical visions of war’s ethical limits (or absence of) and whether their thoughts have contributed to the body of conventions that have evolved to guide war and warfare.
The Just War Theory was asserted as an authoritative Catholic Church teaching by the United States Catholic Bishops in their pastoral letter, The Challenge of Peace: God’s Promise and Our Response, issued in 1983. More recently, the Catechism of the Catholic Church, in paragraph 2309, lists four strict conditions for “legitimate defense by military force”:
- the damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain;
- all other means of putting an end to it must have been shown to be impractical or ineffective;
- there must be serious prospects of success;
- the use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modern means of destruction weighs very heavily in evaluating this condition.