Just war theory has never been more necessary in international affairs, at precisely the moment when some people are questioning its relevance. It is the moral anchor for the international law of armed conflict, without which the law is left to the mercy of the most powerful states to interpret in whatever way suits them. Several recent cases demonstrate what happens when just war criteria are laid to one side, especially the rules about proportionality and the prospect of success. Without a moral basis, international law is too easily manipulated, perversely interpreted or ignored.
A conference at the Vatican, jointly sponsored by Pax Christi and the Pontifical Council for Justice and Peace, has called for just war theory to be reformed in the light of modern circumstances. Some participants would have liked it to be so tightened up as to make war almost inconceivable. That may not be the best approach. Reform needs to take account of the state of international law and of political realities. Just war theory was not devised to banish war entirely, but to make it less likely. That is the more achievable aim.