ABSTRACT
The just war tradition spans centuries; for as long as we have thought about war, we have thought about whether it should be undertaken at all and, if so, how.1 An important progenitor to just-war thinking, St Thomas Aquinas, queried whether war was always sinful and answered in the negative, espousing three criteria by which the justness of war could be established: sovereign authority, just cause, and rightful intention.2 More recent theorists tend to add consequentialist features to Aquinas’s deontological ones. For example, war must be fought as a last resort, there must be a reasonable chance of success, and there must be proportionality between the expected costs and benefits of the war.3 Broadly speaking, though, war should only be fought against aggressors, whether in self-defense or through humanitarian intervention.4
