One important theory within International Relations shows a moral aspect on how to conduct war. This theory is called Just War Theory. Just War Theory is a doctrine of military ethics from a philosophical and Catholic viewpoint. This theory consists of two parts: Jus ad bellum (the right to go to war) and Jus in bello (right conduct within war). Jus a bellum, the right to go to war, explicitly describes how a nation-state should conduct itself before preparing for war.
There are seven sub-categories within Jus a bellum: Just Cause, Comparative Justice, Competent Authority, Right Intention, Profitability of Success, Last Resort, and Proportionality. Just Cause is explained as needing to have a reason to go to war. Not just for recapturing material possessions, but if lives are in danger. Comparative Justice is described, as the suffering and injustice on one side within a war must outweigh the suffering and injustice on the opposite side. Competent Authority must be in order within a war.
Nation-states that start war must only start it if the authorities within the nation-state are focused on justice. Right Intention is defined as; force may be only used for a just cause correcting a suffered wrong. Gaining or maintaining economies by a nation-state is not considered just. Profitability of Success indicates that arms are not to be used where unbalanced measures are pertinent to be successful. The Last Resort category is presented as; force in war may only be used if peaceful alternatives have been completely depleted.
The final category, Proportionality, is the foreseen benefits of starting war must be proportionate to its expected wrongs. Jus in bello, right conduct within war, shows how a nation-state should handle different situations within a war. There are five sub-categories within Jus in bello: Distinction, Proportionality, Military Necessity, Fair Treatment of Prisoners of War, and No Means malum in se (evil within itself). Distinction is described as; nobody in war should attack those not involved in war. No one should bomb civilian areas where there are no military targets.
Also, those in war should not target those who have been captured, surrendered, or do not present immediate threat. Proportionality is the idea that an attack cannot be launched on a military objective in the knowledge that the incidental civilian injuries would outweigh the military advantage. Military Necessity is demonstrated as the use of the most minimal force to limit the unnecessary death of civilians. Fair Treatment of Prisoners of War, under Just War Theory, is important. It prohibits the mistreating or torturing of captured enemies because they no longer pose a threat.
The final category is No Means malum in se. This prohibits the use of evil weapons and methods of warfare including: mass rape, nuclear weapons, and biological warfare. The Just War Theory explicitly details on how war should be carried out by a nation-state. Although war involves deaths and destructions, this is one of the most moral ways to handle warfare. In the world of realism, a thoughtful realist would like to believe that every single one of these categories would be played out perfectly. But, there are many inhibitors with each of these.
A thoughtful realist would not believe with the concepts of Just Cause and Profitability of Success because nation-states need to protect their territories and their economy to stay in their current position of power. Under the concept of Last Resort, a thoughtful realist would agree not to jump into war immediately, but if a major threat were to happen upon a nation-state, it would be necessary. Proportionality within Jus ad bellum and Jus in bello coincides with the views of the realists of stability within a nation-state. Realists understand the effects of war on civilians.
Contrary to Distinction and Military Necessity, Realists recognize that within war there are many casualties and sometimes they are of civilians and those not involved in the war. With terrorist groups of today, a thoughtful realist would say that torture of those captured is sometimes pertinent to safeguard the state. This combats the view of Fair Treatment of Prisoners of War. When the safety of a country is at risk, a realist would agree that it becomes a vital interest. This vital interest could lead to nuclear or biological warfare depending on the severity of the vital interest.
Within the No Mean malum in se category, it overtly condemns this. But a thoughtful realist would agree that these steps might be necessary in some situations. A thoughtful realist would agree with one part of the category, which states that mass rape is completely immoral. A thoughtful realist would want to agree with every statement within the Just War Theory. However, understanding when protection and vital interests are at stake, a thoughtful realist would agree to disregard most of the Just Law Theory to safeguard the country.