[2] The history of jus ad bellum dates back to early religious and philosophical ideas.
There are references to the idea of morally fought wars dating back to ancient civilizations.
[3] Beyond the Egyptians, there have also been tracings of these core just war and jus ad bellum elements in Ancient Mesopotamia, Anatolia, the Levant and Hatti.
[3] Many philosophers in the early centuries have dabbled in defining what is ethically and morally acceptable in war.
Aquinas lists criteria from the Christian perspective that were intended to protect civilians and guarantee that wars were not just fought for the interest of private parties.
[5][6][7] Francisco de Vitoria and Hugo Grotius grew the idea of just war theory into international law.
The League of Nations was one of the first international organization established with a primary goal of maintaining world peace.
"[12] These put the idea of jus ad bellum into writing by requiring states to agree that they will only use armed force in self-defense, or with the approval of the United Nations Security Council.
[13] This may be as a result of the nuance of war in modern times, given the rise of non-state actors such as terrorist groups.
[14] According to the principle of right intention, the aim of war must not be to pursue narrowly defined national interests, but rather to re-establish a just peace.
"[17] A soldier is treated as a prisoner of war and not a criminal because they are operating under the proper authority of the state and cannot be held individually responsible for actions committed under the orders of their military leadership.
However, wars are fought with imperfect knowledge, so one must simply be able to make a logical case that one can win; there is no way to know this in advance.
Diplomatic options, sanctions, and other non-military methods must be attempted or validly ruled out before the engagement of hostilities.