The Myth of the Optional War: Why States are Required to Wage the Wars They are Permitted to Wage

Abstract

If a state is morally permitted to wage a war, is it morally required to do so? A common view within just war theory is that while there are some wars that states are required to wage and, of course, many wars a state is prohibited from waging, there is also a middle category: wars that a state is permitted but not required to wage. These are what we may call “optional wars”. This article argues that that common view is wrong. There are in fact no optional wars. States are either required to wage war or prohibited from doing so. The article assesses the two most promising arguments for the idea of the optional war. The first relates to wars of humanitarian intervention. It holds that if a war of humanitarian intervention would be particularly costly for an intervening state, then that state may not be obliged to wage it. The second relates to wars of national self-defence. It holds that states have the right to defend themselves but that that right is one that can be waived: states are permitted to yield to the aggressors that aggress against them. The article refutes both arguments. Pace the first argument, states should not wage wars when the costs of doing so are overly burdensome to their citizens. Pace the second argument, states owe it to both their citizens and other states to resist aggressors whenever they are morally permitted to do so.