A. Ad bellum principles:
1. The cause must be justified.
2. The intention must be right.
3. The war must be waged by a competent authority.
4. The war must have a reasonable probability of success.
5. It must be fought only as a last resort.
B. In bello principles:
1. Non-combatants, neutrals and third parties cannot be harmed.
2. Existing laws and treaties, e.g., the Geneva Conventions, must be honoured.
3. The means must be proportionate to the goals.
4. The enemy must know the terms on which peace can be achieved.
5. The goal must be the return of the aggressor to a rightful place among the nations, not its extermination or subjugation.
It's important to recognize that some evil is beyond redemption and must be destroyed to prevent further carnage to the innocent. The Nazi government in WW2 was destroyed, but Germany rightfully retained her status as a nation, free of that evil. On the other hand, ISIS is not a recognized nation, but a movement (caliphate) that seeks to extend itself into nations worldwide. As such, "in bello" principle 5 does not apply and ISIS is an example of a pernicious evil that is beyond redemption and must be destroyed.