Thomas Aquinas' writings on the "Just War Theory" from Summa Theologie are worth some study. Some general principles:

War is justified (nation A wars justly against nation B) on the following conditions:

1) It is called by a sovereign authority.
2) It has a just cause.
3) The combatants have morally right intentions (not vengeance or profit)

Qualifying Conditions (from the theory of double-effect on his justification of killing in self-defense: ST II-II, 64, 7).
1) Cannot intend intrinsically evil actions.
2) A good action, or at least a morally neutral action, will have two effects: a good intended, and an evil, not intended, but tolerated.
3) Proportionality: the good to be achieved outweighs the evil of war.

#peace
#war
#prayforpeace
#christ