But this isn’t simply a question of strategy. Lots of stupid things are morally justifiable — running into a building to save your child even though you have no fire-retardant gear or relevant training if there is no time to contact the guys in red hats, say. Trying to wage a war when you have not satisfied the necessary conditions for justice is not one of them.

The Catholic Church’s teaching on just war is admirably clear and cogent. Guiding it are four principles outlined in the catechism. The first is, very obviously, that so far from being pre-emptive, the war must be waged in response to another’s aggression; the harm inflicted on the nation considering retaliation “must be lasting, grave, and certain.” The second is that diplomatic means of resolving the situation must have been thoroughly exhausted. Third, “there must be serious prospects for success.” Finally, since the goal of a just war is the restoration of peace, “the use of arms must not produce evils and disorders graver than the evil to be eliminated.”