Just War Principles

NOTE: The following is an excerpt of an article in the New Catholic Encyclopedia, 2nd Edition, published by the Catholic University of America (2003). See volume 14, pp. 637-644.

The term 'just war' is employed to refer in a shorthand way to the set of norms or criteria for assessing whether a government's recourse to force is morally justified. The just-war tradition is expressed in many forms: in international law, in the codes of conduct of national military forces, in moral philosophy and theology, in church teaching. The just-war norms embrace two sets of criteria. One, the ius ad bellum, identifies criteria for judging whether the resort to force is justified. These are sometimes called the 'war-decision' rules. The second set of criteria, ius in bello, regulates and limits the use of force in combat. These are sometimes called the 'war-conduct' rules.

Ius ad bellum. The ius ad bellum contains six (or seven) criteria to determine whether resort to force is justified. They are: (1) just cause, (2) competent authority, (3) right intention, (4) last resort, (5) probability of success, and (6) proportionality. To these is sometimes added the criterion of comparative justice, which assesses which of two adversaries is 'sufficiently right' to override a presumption against the use of force.

Just Cause. According to The Challenge of Peace, "War is permissible only to confront 'a real and certain danger,' i.e., to protect innocent life, to preserve conditions necessary for decent human existence, and to secure basic human rights."

Defense against Aggression. For much of the 20th century, the sole justification for war was taken to be defense against aggression. That definition, however, proved too narrow to deal with a variety of conflicts that emerged in the late 20th century, especially guerrilla warfare, terrorism and counter-terrorist campaigns, and ethnic cleansing.

During the Persian Gulf War, the Vatican made an attempt to narrow the definition to defense against 'an aggression in progress,' a formula that would have precluded a Coalition attack against Iraq and would have allowed that country to retain the fruits of its aggression in Kuwait. In the wake of the terror attacks against the United States on Sept. 11, 2001, while repeatedly warning against a war of religions and urging forgiveness, Pope John Paul II declared that there is 'a right to defend oneself against terrorism, a right which as always must be exercised with respect for moral and legal limits in the choice of means and ends' (World Day of Peace Message, Jan. 1, 2002).

Humanitarian Intervention. The ethnic cleansing that accompanied the breakup of the former Yugoslavia and the wars in Croatia (1991-1992), Bosnia (1992-1996), and Kosovo (1999) led to the emergence of 'humanitarian intervention' as a new criterion of just cause. According to this norm, the international community or, as a last resort, any nation with the capacity has 'the right and the duty' to intervene militarily where, in the words of Pope John Paul II, 'the survival of populations and entire ethnic groups are seriously compromised.' Though humanitarian intervention entailed overriding the established international legal principles of national sovereignty and nonintervention, in a short time Pope John Paul II's declaration that 'states no longer have a right to indifference' prevailed. Humanitarian intervention became in practice a recognized, though not unquestioned, just cause.