Why do just war principles require that force be a last resort and proportionate to the threat?

Just war theory, which provides a framework for the ethical use of armed force, mandates that war be a last resort and that force be proportionate to the threat to uphold the moral imperative of minimizing human suffering and preventing unnecessary destruction.1

The requirement for force to be a last resort ensures that all peaceful alternatives—such as diplomacy, negotiation, or economic sanctions—have been exhausted before resorting to the grave consequences of war. This principle reflects the ethical commitment to preserving life and stability whenever possible.1

The requirement for proportionality dictates that the force employed must be commensurate with the threat faced and the objective sought. This prevents the escalation of conflict beyond what is necessary to address the initial injustice or danger. By limiting the scale and intensity of military action, proportionality serves as a critical restraint against excessive violence, ensuring that the anticipated benefits of the intervention are not eclipsed by the resulting costs and devastation. These principles are essential for maintaining the distinction between a just response to aggression and the perpetuation of further injustice.1