The just war tradition and its modern legacy: Jus ad bellum and jus in bello

The relationship between jus ad bellum and jus in bello has been characterized differently throughout European history. There have been three main positions exemplified by Hugo Grotius, Samuel von Pufendorf and Emer de Vattel. They are, first, both the cause and the conduct of warfare must be just; second, the cause must be just, but the conduct of the war is unconstrained in order to achieve the goal of peace; and, third, we must assume justice on both sides, and concentrate on ensuring just conduct in armed conflict. Each attempted to distil customary practices, which they saw in some relation to Natural Law, the ultimate source of moral obligation. Customary international law now serves the function of Natural Law in that even if treatises in which it is articulated lapse the customary constraining precepts remain, and are equally obligatory. It is contended that the relationship between just war and just conduct in war during the 20th and 21st centuries has mirrored the three classic positions, and since 9/11, with the advent of new dimensions to warfare in the war against terror, the relationship is in flux. Since 9/11 there has been a growing emphasis on jus ad bellum and a relative silence on the principles of jus in bello. Implicitly, there is an informal acceptance of something like Pufendorf’s position in which outlaw combatants are deemed to place themselves outside of the protection of customary law