Just War Theory
Just War Theory consists of two primary components, first determining if a war may be justly conducted (jus ad bellum) and how it must be conducted (jus in bello). It is based largely on the work of Augustine.
Jus ad bellum - Is a war just?
Under jus ad bellum, only legitimate authorities can wage war for the right reasons (usually this means a defensive war) and only as a last resort if every other peaceful means to avert war have been used to no avail. A just war can only be waged if there is a serious evil that needs to be stopped. Further there must be a realistic chance that the evil can be stopped without starting a greater evil. If this happens the war reaches a just conclusion. A war started for just reasons and justly waged may still reach an unjust conclusion.
Jus in bello - How must a just war be conducted?
Minimum force should used be to achieve just goals. Civilian areas without military target should not be attacked. Force used should not be out of proportion to the wrong which the war tries to right. Efforts should be made to minimize casualties, especially civilian casualties. The enemy are also people.