We asked some renowned moral theologians from different countries with ties of friendship to the Alphonsian Academy to write a post for our Blog. Our request to them was to write a comment on Fratelli tutti, nn. 256-262, by Pope Francis – these paragraphs discuss the very topical theme of the injustice of war. This is the fifth contribution of the series. Pope Francis returns to a frequent theme of his: «War is the negation of all rights and a dramatic assault on the environment. […] We must work tirelessly to avoid war…» (FT, n. 256). It is not an original idea in papal teaching. However, Pope Francis concretises it with a particular assessment of current circumstances. He notes in paragraph 258 that «in recent decades, every single war has been ostensibly “justified”». He concludes that «it is very difficult nowadays to invoke the rational criteria elaborated in earlier centuries to speak of a “just war”». Does this imply a development of the just war theory, or is it an appeal to replace it with a moral principle? The four conditions of just war theory are repeated in The Catechism of the Catholic Church (n. 2307). It leaves evaluation for…