Thanks for asking.
I'll start by saying that I'm only aware of one
clean humanitarian intervention ever, since the idea has come into play and that was the intervention by the French, approved by the UN Security Council (UNSC), in April 2011. But this one was even legal, because approved by the UNSC.
Legally speaking there's only a right to defend one's self from the threat or use of force or to protect another from that. A threat has to be imminent and clear, not something that might happen or still far off. For any other reasons, including humanitarian intervention, approval from the UNSC is required. That's the legal answer.
We all know the UNSC is a political body and that its permanent members will block resolutions if they concern political allies. The UNSC can therefore fail to intervene where intervention would be appropriate. This has given rise to a body of work with respect to humanitarian intervention in literature and humanitarian intervention in practice. The latter is crap, the former has a lot to say for it depending on what you read (I don't recommend Hippyhead or Paul Edward's posts obviously).
A humanitarian intervention is broadly the use or threat of force against a State in order to protect non-State groups or people from some type of substantial breach of their human rights. There's a movement to get this codified as part of the UN Charter (The Responsibility to Protect) - and therefore shouldn't be confused as a roadmap for individual states to intervene without UNSC approval - others base themselves on customary international law, or consider it illegal. If they consider it illegal then there are those who say sovereignty trumps human rights and those that believe it can be illegal to intervene but that this may be excused because it protects a higher cause.
I'm personally inspried by the just war doctrine to qualify sovereignty. I'm reaching back to some old work again to explain my thoughts on the subject of "right authority", which equally applies to sovereignty:
It is the care of the common weal that is entrusted to those in authority and it is therefore their business to watch over the common weal of a community. And as it is lawful for them to use the sword, as Aquinas put it, in defending this common weal against internal disturbances so too is it their business to wage war in defending the common weal against external enemies.
Quoting Augustine he says: “The natural order conducive to peace among mortals demands that the power to declare and counsel war should lie in the hands of those who hold the supreme authority.” It is important to stress the requirement of supreme authority. It would seem that any authority that can turn to a higher authority for arbitration is not allowed to declare war. However, the possibility that seeking redress might fail because the highest authority is ineffectual in enforcing its decisions begs the question whether a lower authority is then allowed to declare war. It appears to me that the ability to enforce decisions is inherent to Aquinas’ idea of authority, since he does not consider this problem. What, then, is an acceptable way of defining authority?
It is suggested for the purposes of my analysis that an authority is a body, which is entrusted with the care of the common weal and has been given the power to use force in accordance with the consensus of the relevant community that transferred its ability to use force to the authority.
“In accordance with” denotes the fact that nobody subjugates himself body and soul to a sovereign or State, for there exist statutes that confer definite powers to an authority to administer and provide an order of coexistence in which everyone can do as he wishes as long as he remains within the system that is created for everyone’s secure and safe interaction and interdependence. It is undeniable that the object when instituting such authority is to subject the exercise of power to a rule of law.
The relevance of a community relates to the extent it has the ability to use force against other communities and impose its will on those other communities and its ability to transfer the use of force. A supreme authority is therefore never part of any community. In a democracy the relevant community is the electorate, who are a part of a larger nation. In a medieval kingdom it were the king’s vassals, but the kingdom consisted of peasants and workmen as well. Although the described process seems democratic it is of course possible that the relevant community is a powerful minority within a greater whole. This is sociological legitimisation of authority and as such it is unconcerned with the objective good of the authority.
Illegitimate authority is then authority that has lost its legitimacy because of the development of one or more new relevant communities that vie for enforcement of their will with the established relevant community. This will mean that at that time there is no relevant community that can transfer power for no one community has at that time the ability to impose its will on others or prevent others from wilful exercise of force within their community. Once the fog of such civil war lifts sufficiently to enable some understanding of the new balance of power, it is entirely possible that several new authorities are created dependent on the progress and/or the outcome of a war. The authority can also be illegitimate because of a lack of consensus within the relevant community in the sense that not enough subjects of the relevant community recognise the authority. In either case, there is a fundamental absence of legitimacy for the authority does not represent the relevant community or a community’s majority. The authority might well continue to exist and exercise power, but it has lost its legitimacy.
I would suggest another term for an authority to which no powers or only partial powers have been transferred. I consider this to be imperfect authority. For example, such authority can have religious, scientific or traditional authority but it has no instruments or too little instruments to enforce its rules. Imperfect authority can also be the result of the development of new problems to which the authority has not been adequately equipped to deal with. It is then the business of the relevant community to create new instruments for the authority to handle such problems, as it is their business to decide to which rules of law the authority’s powers are subject.
Considering that it is easier to control that which is close at hand, there must be a convincing reason why the parts that make up the relevant community are willing to transfer their ability to use force. When we consider the use of force necessary to be able to impose one’s will on others, two processes become apparent. If one person imposes his will on others, these others will have lost their freedom insofar as this person chooses to exercise force to impose his will. These others are then faced with two options, either acquiesce to these circumstances, which do not necessarily have to be bad circumstances, or oppose them in a combined effort, assuming that each separately does not have enough strength.
Instead of having one’s freedom dependent on the way the person in “power” exercises force, a level of freedom is guaranteed by transferring (a part of) the ability to use force to a common authority able to protect the community against the wilful exercise of force by an outside third. On the other hand, acquiescence will create an authority, which is not necessarily illegitimate.
The other process is similar to that of conflict settlement. In conflict settlements disputes are sometimes brought before an objective third party. This third party, however, can also be created from the ranks of the disputing parties. In this process, it is the authority itself that enables the relevant community to reach consensus and diminish strife. Both (or more) parties protect themselves against each other’s wilful exercise of force, which is now transferred to the authority and bound by the rules these same parties instituted when forming this authority. The purpose, for which authority is instituted, is therefore the protection of the community against the wilful exercise of force.
The protection against wilful exercise of force must then inter alia be the authority’s primary duty. If the authority fails in its primary duty, it fails in its care of the common weal. The relevant community that instituted it automatically assumes this duty as there is no other community – not considering the development of one or more new relevant communities – that has the ability to provide this protection or any community necessarily willing to do so. Also, it can be argued that the relevant community that instituted the authority is primarily responsible for the authority’s functioning for it is this community that subjected the authority’s exercise of power to rules of law. If the authority lacks the powers to fulfil its primary duty and this is caused by its imperfection then the relevant community is responsible. Either way, if the authority fails in its primary duty then it loses its singular right to exercise force. As long as the authority has the powers to fulfil its primary duty and effectively does so it retains this right in principle. This is what I will say of authority, its legitimacy and its ability and right to exercise force. — Moi
Can a sovereign nation lose its sovereignty? I think it can and I believe there is where the gap lies in which humanitarian interventions should be allowed. But it takes quite a bit before it does so. And that's because, if we're talking about oppression this is a vague concept. Are the Chinese oppressed? How about Hong Kong citizens? Or for the communist minded among us, how about the poor in most capitalist societies?Torture might happen (Guantanemo) but it may not be systematic or at a large enough scale. How about not being able to appeal court cases? Strictly speaking a breach of due process and therefore a gross breach of human rights but does it warrant intervention? So which human rights abuses and how bad should it be before we should even start considering to act? This is not something with an easy answer from a moral point of view. From a political one it is too easy, leading to abuse. Whatever the answer, it's clear that we should judge on a case by case basis.
Problematic too is to find an alternative authority within the relevant community to take the place of the illegitimate authority in a manner that not only makes it legitimate but also effective. It won't do to simply occupy and impose a new system on people. So even if we are talking about an illegitimate authority any intervention must ensure it reaches the goal of establishing a new authority as well. If it's absent, your have no business intervening unless we're talking about genocide.
Aside from such considerations of course the intervening party should have the right intention and the situation his use of force introduces should be an improvement over what it tries to stop and the war itself should be less bad than the situation itself. An intervening party should also use force only as a last resort, especially because we are here not speaking of imminent threats or actual use of force at scales we understand to be conventional war. And finally, the action needs to be proportional.
That's more or less my take on it.