The Just War Theory
The very idea of war can seem antithetical to Christianity since the Fifth Commandment is often translated, "You shall not kill." However, the text reads, "You shall not commit murder." Sometimes, killing is justified. Therefore, sometimes war is justified.
It's never pretty, of course. And, as Pope Francis said recently, "War is always a defeat." Nevertheless, there are times when justice itself demands that a country go to war, lest its people permit evil to go unchecked and the oppressed undefended.
Nor is the mere absence of conflict what makes for peace. I believe, for example, Our Lady and Saint John were at peace while at the foot of the cross, even as they were surrounded, as it were, by conflict and violence. Their hearts were at peace.
God is concerned with the intentions of the heart, and He looks poorly on the intentional taking of human life (Catechism, #2307). However, each of us has the right to protect his own life, even through the use of force. This means that although an act of self-defense may have a two-fold effect - the preservation of our life and the unfortunate taking of the aggressor's life - the first effect is intended, while the second is not.
With regard to nations, "governments cannot be denied the right of lawful self-defense once all peace efforts have failed" (Vatican II, Pastoral Constitution on the Church in the Modern World, #79). The Just War Theory of the Church establishes the parameters for the waging of war, and for seeing it through to its completion. It can be found in the Catechism of the Catholic Church (#2309), and it reads as follows:
(1) The nation must have a just cause. Its self-defense must be against an unquestionably grave danger. "The damage inflicted by the aggressor or the nation or community of nations must be lasting, grave and certain."
(2) War must be the last resort. All other reasonable peaceful alternatives (i.e. negotiation, mediation, embargoes) must have been found to be ineffective. Here we see the importance of an international mediating body, such as the United Nations. The Catholic Church, for example, has a diplomat of the Holy See in almost all of the world’s embassies.
3) There must be a reasonable prospect of success. The achievement of a war's purpose must be based on the real possibility of victory. We don't send young men to their certain death. We are not terrorists.
(4) Finally, the war must respect proportionality. The use of arms must not produce evils graver than the evil to be eliminated, as when a state leaves an aggressor’s country in total devastation. Modern means of warfare give great weight to this criterion.
The Catholic Church bids us to apply such criteria to our judgments, instructing and guiding us with the authority of Christ, but leaving us also free in our decision making. Instead of imposing rules and laws, the Church proposes principles for us to apply to our discernment of world events, principles which help us to see by the light of truth. +