Ryan Jenkins from 1000-Word Philosophy gives an account of just war theory.
War is a profoundly destructive institution, yet most of us still believe there are good wars. Authors as far back as Cicero, and in various cultural traditions, have sought to answer this question: When is a war just? The just war tradition (or just war theory) is one subset of military ethics. Recently, interest in just war theory was ignited by Michael Walzer’s Just and Unjust Wars (2006), published in the wake of the Vietnam War. More recently, profound challenges to “traditional” just war theory—under the banner of “revisionism”—have shaken the foundations of the ethics of war (McMahan, 2009; Rodin, 2005). This article will explore the criteria of traditional just war theory before briefly discussing the revisionist school’s recent critiques.
Jus ad Bellum: Justice in the Resort to War
Traditional just war theory concerns itself with two questions: (1) when it is just to go to war and (2) how may a war be justly fought? (These two areas usually go by their Latin names: jus ad bellum and jus in bello, respectively.) This way, we can say that a war was just to declare but fought unjustly, or perhaps vice versa.
When is it just to resort to war? (Notice this moral question is separate from when war is prudent or popular.) Traditionalists hold that a state must satisfy several criteria: just cause, right intention, last resort, proportionality, probability of success, and proper authority.
Theorists usually think the only just cause for declaring war is self-defense: that is, as a response to an actual aggression. Pre-emptive war—declaring war on a state because it is believed they will be a threat—is clearly a Pandora’s box. Instead, we must meet a high evidential burden in order to justify war, and a merely suspected attack is not enough.