Believe it or not, there are quite a few sources on the subject. However, if we are wanting to hear the Apostolic, or rather, the teachings that were handed down from the Apostles, we need only ask the Doctors, Fathers, and Saints of the Church. For example, it was St. Augustine who was the founder of the “Just War Theory” in the Western tradition. In fact, in St. Augustine’s Contra Faustum Manichaeum, “Augustine argues that Christians as part of government should not be ashamed to protect peace and punish wickedness.” St. Augustine is also quoted in Augustine: Political and Social Philosophy , “by divine edict, have no choice but to subject themselves to their political masters and [should] seek to ensure that they execute their war-fighting duty as justly as possible.” It was really a kind of guideline for when war can be justifiable against nations and it was among these guidelines that helped to clarify the proper conduct of war as opposed to genocide and outright tyranny. According to St. Augustine, two aspects of the Just War Theory had to be met, “the Right to go to war” and the “moral conduct of war”. In the moral right to go to war, there were also sub-category aspects that needed to be met. For example, there needed to be a just authority that legally deliberated on the matter through just and lawful means. Also there had to be a just cause as in the need to stop terrible genocide or the spread of other inhumane or otherwise destructive forces threatening to conquer all people. St. Augustine also argued there had to be a proper intention as well. A good example of proper intention to go to war is to simply stop the destructive force and thus bringing the war to an end. And finally, the need to go to war can also be decided as a last resort as every single option to avoid war has been exhausted but to no avail.