What are at least two criteria for deciding on armed intervention and to what extent do they conflict with each other?
For the free world, armed intervention should be reserved for a situation in which the major powers are in agreement that war is justified. I don't believe a country should ever act alone in declaring war.
An exception would be a direct military attack on a non-aggressor country. In that event, the country would be justified in counterattacking and thereby declaring war on the attacking country.
War can be in self-defense (as in the above example), or a a police action. The justification for police-action form of war is problematic. There needs to be consensus among free-world powers. In contemplating a police-action, it is important to distinguish geopolitical/ideological/cultural differences from out and out criminal behavior by a proposed target country.
I think #3 best picks up on the dilemma between armed intervention in response to a tangible military threat and then armed intervention in response to humanitarian needs. Of course, as history has shown, both can result in far more trouble in the long run than not intervening in the first place. Afghanistan is of course an excellent example of this.
Three internationally recognized criteria for armed intervention are (1) whether the projected war can be won and (2) whether the cause of war is just and (3) entered into with right intention. There may be a conflict an armed intervention has a just cause and a right intention but has no prospect of a successful outcome without the use of disproportionate measures. Just cause and right intention seem not to present a conflict.
Is there a direct and obvious threat to national sovereignty and security, e.g. are your border being threatened or crossed, or your citizens killed or harmed by an aggressor? Another criteria, and this is one tragic failure of the Iraq and Afghan conflicts to me, is that in order to enter a war, I believe you should have an exit strategy, including clear goals you are seeking to achieve, otherwise we end up in protracted conflicts that tax our resources and our military excessively and unnecessarily.
It used to be so simple: Armed intervention would only occur if (1) a nation's citizens were in danger; (2) a nation's borders were compromised; and/or (3) if a nation's allies were threatened. In the case of the U.S.'s recent international military interventions, the only valid reason for such a scenario would entail only the third option. Now, as the world's policemen, the U.S. must also consider other reasons such as humanitarian aid, ethnic cleansing, nuclear instability, and protecting valuable oil reserves. Our government will no doubt find other reasons to make such excursions in the future.
Two possible criteria are humantarian needs and needs based on power. In other words, we might go to war to protect people or we might go to war (or not go to war) based on what is most likely to increase our power.
These two criteria can certainly conflict with one another. The most common conflict is in cases like that of Libya today. There is, arguably, a real humanitarian case for going to war more vigorously than we have. On the other hand, an all-out US involvement in this conflict is likely to reduce our power and security rather than enhance it. In this way, different criteria for armed intervention/war can give us different answers as to what we ought to do.
I think that you are going to see different answers to this question. It makes sense because there is really no right answer to it. Different leaders have used different criteria. Some have been successful while others have not been. In the end, some threshold for military intervention is needed and to this end, I think that there are some definite instances where military action is warranted.
I think that I believe that if there is a coalition of nations willing to share the cost and the burden of military intervention, this becomes on criteria I would use in my calculus. The globalized world has made it so that nations must recognize the need to act in concert with one another. Given how so many of the realities of the globalized setting impact everyone, unilateral action that alienates, as opposed to brings in seems to be something of the past. I think that if multiple nations can combine and coordinate efforts in understanding the need to commit armed forces, it helps brings credence to the cause of the fight and helps make the need to commit troops something that more people can find agreement.
I think that I would use a humanitarian standard to determine intervention. If there is ethnic cleasning or genocide on a massive scale being perpetrated, I believe that there is a need for intervention. If a leader is gassing or killing his own people in an attempt to consolidate power, I think that military intervention is warranted. It pains me to say this because I think that humanitarian causes are binding ones, but in operating within the realm of what criteria should be used to justify intervention, I would say that humanitarian violations would be a good enough reason to warrant military action.