Well, what is moral and what is just aren't exactly the same thing, but Aquinas laid down his idea of what constitutes a just war a long time ago. I think that might have been what Obama was shooting for. Here are the factors:
1. It has to be waged by the state, and not individuals. War concerns the well-being of all the citizens, not just a few citizens, so it's the state's role to decide when and how to fight a war.
2. The target of war has to have it coming for some reason. "A just war is wont to be described as one that avenges wrongs, when a nation or state has to be punished, for refusing to make amends for the wrongs inflicted by its subjects, or to restore what it has seized unjustly."
3. The aggressors must have good intentions, rather than being motivated by greed, bloodthirst, or "cruel vengeance."
Other thinkers have refined the idea and added new criteria over the centuries. Such as these:
4. Proportionality. The benefits of the war have to outweigh the costs of the war. You don't send in the bombers just so that you can get your captured pilot back.
5. The aggressor must have a reasonable chance of success without using disproportionate measures.
6. Last resort. All chances at a peaceful resolution of the problem need to be exhausted.

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