This is why historic Christianity can give us a backbone. Thank St. Augustine of the 4th Century for giving us a spine.
Long read hut worth it. There are some opinions on modern war that I left out. You can find that in the link. But here is a good read for Judeo-Christian Worldview types.
Maybe some day we will produce a leader who has honor as a result of reading this article.
"The way we think about the legitimacy of war has its origins in the thought of St Augustine. He believed that the Kingdom of Peace cannot be realised within human history, only beyond, therefore we have to reckon with the reality of sin, including violence, and the possibility of war. Yet despite this reality, he had a deep abhorrence of war and so he wanted to develop a tool to assess the morality of wars in order to limit their number and brutality, and to protect the moral order of the world. This tool took the form of a set of conditions to be satisfied for a war to be considered just what we have come to know as Just War Theory. This theory remains the primary moral framework for questions of military intervention by States, both for Christians and more generally. For example, when an international commission was asked to define the 'Responsibility to Protect' and set out the conditions for humanitarian military intervention, it used the criteria set out in traditional Just War Theory.[1]
Criteria for a Just War
Augustine's criteria were developed by Thomas Aquinas and there have been various subsequent amendments [2], and the criteria were substantially examined by the Catholic Bishops of the USA in 1983.[3] The presumption of the theory, in keeping with Augustine's stance, is against war. The theory falls in two main parts: jus ad bellum, which is concerned with the ethics of declaring war; and jus in bello, concerned with conduct during war. (Today, ethicists have increasingly been talking of jus post bellum, concerned with the conduct of the victorious party after the war.) The criteria can be summarised as follows:
Jus ad bellum
1. Wars must be fought only on legitimate authority. This criterion aimed to limit conflicts by small-scale barons, captains and princelings, and is often treated as the sine qua non of Just War Theory. [4]
2. The cause must be just. The war must be fought, for example, in order to resist aggression, protect the innocent, or to support the rights of some oppressed group. There must be significant reasons which are weighty enough to overthrow the prima facie duty that we should not kill or injure others.
3. The war must have right intention. It must advance the good and avoid evil, have clear aims and be open to negotiation; it must not be for revenge or for the sake of killing and there should be no ulterior motive. It must be waged without love of violence, or cruelty; and regret or remorse should be the proper attitude. This is shaped by the pursuit of a just cause. Since peace should be the object of war, killing is a means to that end. This condition also holds for jus in bello.
4. It must be a last resort, all other attempts having failed or being unavailable.
5. There must be a reasonable hope of justice, or a reasonable chance of success, in order to prevent pointless wars. If there is no such hope, then it would not just be imprudent, but there would be no good grounds to override the prima facie obligation to not harm others if none of the just ends can be realised, and thus going to war would be immoral. [5]
Jus in bello
6. There must be discrimination. Non-combatants should not be directly or intentionally attacked, although it is recognised that there may be accidental casualties.
7. There must be proportion; that is, there must be a balance between the good achieved versus the harm done. This condition takes into account the effects on all human beings, not just those on one side, and it is the effects on humans rather than other physical damage which have priority. This condition also applies to jus ad bellum, in order to prevent going to war over minor disputes.
A just war, then, is not a war in which both sides act justly; in fact there cannot be such a war. For a war to be just, that war must be waged in order to right a wrong or to prevent an imminent injustice.
The Basis for Just War Theory
There is general acceptance that killing is, all things being equal, a grave wrong. John Rawls argues, for example, that we have a 'natural duty' which is owed to persons generally not to injure or harm others. [6] Christian theology derives the same obligation from the Decalogue and more generally from the norm of agape. [7] It is necessary then both to demonstrate that the prima facie obligation not to kill or injure others is overridden in the case of a just war and that the innocent [8] are not being directly killed.
The demands of justice are such a case. For example, outside the room in which I am writing there is a playground full of children. If someone came into the playground and started to attack the children and if I had a rifle by the desk, I would be justified in shooting the assailant, even though I myself may not be at risk. The classical natural law of justice, which is viewed as superior to the laws and demands of any State, sees all people as brothers and sisters who share in the cosmic logos and thus we are required to treat each other with the justice and respect owed to all. [9] Implicit is a concept of human solidarity, according to which we have mutual obligations and duties to all people. Roman law also involved contractual obligations which entitled one to protect the rights of others and seek redress from those who cause the individual or State injury or harm.
Just War Theory is based on this classical view and from it the central concepts derive: that of the prior guilt of the offending party; and of just war as a means of vindicating violated rights or a violated order of justice, or as the means of restoring justice. However, the enemy's natural rights must be protected since they are also humans and must be treated with justice and respect, even after hostilities have begun. Hence conduct in war must be just. [10]
The decision to go to war is not made simply on the basis of the enemy's deeds, for example being unjust or violating international law, but also on one's own intentions: they must be upright in terms of both means adopted and ends pursued. Moreover, all the aims and intentions must be included. It is not permissible to use some just intentions to justify the pursuit of other unjust intentions. Thus clear objectives are required. Intent, however, is complex; moreover, outcomes of wars are notoriously unpredictable: they rarely achieve their political objectives unambiguously and often become the cause of future wars.
Prima facie obligations
Killing is a prima facie wrong and always stands in need of justification: without justification on moral grounds it is an actual wrong. Killing, then, is never morally neutral: according to Frankena, 'even when they [the killers] are justified there is still one moral point against them'. [11] So Just War Theory in effect deals with a moral dilemma: there are two prima facie obligations to avoid killing and to meet the demands of justice and one cannot be fulfilled without sacrificing the other. The dilemma is resolved by finding justification for sacrificing one in favour of the other and the criteria are the means by which one decides. Just War Theory starts with a presumption that war is prohibited and is not justified unless it can be demonstrated as such, and then specifies situations in which use of force would be justified. However, the burden of proof rests on the person who intends to go to war.[12]
The distinction between prima facie and actual obligations is important. The argument is that what appears to be a conflict ceases to be so once the situation is correctly analysed and the actual obligations become clear. [13] 'To hold that an obligation or duty is prima facie is to claim that it always has a strong moral reason for its performance, although this reason may not always be decisive or triumph over all other reasons'.[14] So, other things being equal, a prima facie duty is normally binding but, unlike an absolute duty, it does not necessarily determine one's actual obligation.
Just War Theory provides for situations when the prima facie obligation is overridden. However, the obligation is not cancelled and continues to exert influence, particularly in jus in bello. Specifically, the theory states that the aim should be to restrain or incapacitate, rather than kill or injure; that unnecessary suffering is excluded; that aggression is only directed towards combatants when they are a threat (that is, they cease to be a legitimate target once they surrender or are injured), and that attack on non-combatants is wrong or unethical. In this sense there is a distinction between the person qua person, and the person qua soldier. [15] Moreover, any indirect or incidental effects on non-combatants must be justified by proportionality.
So in certain circumstances it is legitimate and necessary to override some prima facie duties in favour of others which have a stronger claim and take priority, such as to uphold justice or to protect the innocent. War, therefore, can be a moral undertaking and the State has the right to go to war, but it remains subject to moral principles and rules determined by the overridden prima facie obligations."
https://www.thinkingfaith.org/articles/20131011_2.htm 
