Nigel Biggar tackles the question: has just war theory ever prevented a war?
Has just war thinking ever been used to decide not to go to war? Whilst I think about that, let me ask a slightly different question: has just war thinking ever been used to criticise a war? Certainly. So you’ll find in the 16th century, for example, the Spanish scholastic moral theologian Francisco de Vitoria writing very critically of the conduct of the Spanish conquistadors in the Caribbean. And Vitoria was a just war theorist, arguing that it’s not justified to war against a people just because you want to impose the benefits of your religion on them, for example.
Certainly, just war theory has been used to criticise wars, and in recent times lots of people have used just war criteria to argue that going to war in Iraq was wrong, or going to war in Syria (against Islamic State in Syria) is wrong. In the case of the UK, those arguments didn’t prevail – but you’d find other people on the other side also arguing that going to war in Iraq was right, going to war against ISIL in Syria is right. So I can’t think of a war that has actually [been] prevented but I can certainly think of wars where critics have used just war thinking to influence public opinion.