If I understand Geoff well, in the setting of a non-international armed conflict - a common article three conflict - unlawful belligerency is not itself a violation of the (international) laws and customs of war, although it might and probably is a violation of the state's domestic law in which the armed conflict takes place. I agree with Geoff that I'm not aware of any precedent finding a participant in a civil war guilty of a violations of the laws and customs of war as such for unlawful belligerency (I've never looked through the Yugoslavia case law on this, but I would guess it would be the same). And it makes sense in the non-international armed conflict circumstances - if it were a crime in non-international armed conflict, then everyone who takes up arms would automatically be in violation of an international law rule. Whereas we normally assume that international law is silent on the subject, and that domestic law carries, including prohibitions on rebellion, insurrection, etc.
Another way to put this, perhaps, consistent maybe with Geoff's earlier post that I've put up on this blog, is that you only get to Article 4's definitions of a combatant if you are an Article 2 conflict. CA3 is self-contained, and just as it contains no reference to grave breaches, likewise it contains no definition of legal or illegal combatancy. On this theory, then, if you commit certain acts, you have (criminally) violated CA3, but not in virtue of having fought even as a member of a group that fails the Article 4 tests of adherence to the laws of war, responsible commander, carry arms openly, etc.
But the one question I would have for Geoff is about these requirements under Article 4. If it is the case that you can't be an unlawful belligerent - of course you may commit specific crimes against the laws of war, but you can't be defined as an unlawful belligerent punishable as such because you are outside the reach of Article 4, to which you only get via Article 2 - what about the specific requirements of Article 4. They are treated in Article 4 as definitional elements required in order to achieve the status of legal combatant entitled to the combatant's privilege. And in an international armed conflict, if you fail to meet them but then undertake direct participation in hostilities, then you are an unlawful belligerent.
But in that case, what about not carrying your weapons openly, not wearing visible emblems, fighting with a group that systematically violates the laws of war, etc. - are those separate violations of the laws and customs of war, even for participants in a CA3 conflict, separate from their role in the criteria of defining a combatant in an international armed conflict? Could one separately charge those as crimes in themselves in a Common Article 3 conflict? I believe that one can, and that it is consistent with the reason why they are featured as definitional elements of Article 4 - because they are crimes that are indicative of a systematic failure to follow the laws of war. Article 4 has them because they are already customary law crimes. Geoff, am I right about this, or missing something about CA3?
I particularly agree, by the way, that if unlawful belligerency were automatically a crime in a non international armed conflict, the asymmetry would create very undesirable distortions in incentives and reciprocity in actual fighting.
Here is Geoff's comment:
Why is it not a defined offense? I suspect that this is simply an efficiency decision. It is likely that once the proponents of the commissions realized that offenses would be statutorily defined, and subject to trial by commission by statute, they decided it was easier to just criminalize the underlying conduct and not the status. Plus, I am not sure that there is total consensus that being an "unlawful belligerent" in the context of a non-international armed conflict is a distinct offense in violation of the laws and customs of war.
I have struggled with the "offense" of unlawful belligerency in the context of a non-international armed conflict. I have come to the point where I am just not ready to concede that this is indeed an international law "crime" in violation of the laws and customs of war.
I don't dispute that fighting as an unlawful belligerent is a settled violation of the laws and customs of war resulting in criminal liability in the context of an international armed conflict. However, it seems to me that this criminal liability creates a deterrent that reflects symmetry with the benefit of combatant immunity derived from fighting as a lawful belligerent in such a context. But because it is essentially impossible for a non-state actor to be a lawful belligerent in a non-international armed conflict, it seems to me the deterrent symmetry of the law is inapposite to such a context.
I realize that such a non-state actor can’t be a lawful belligerent in a non-international armed conflict. But I think all this means is that such an individual is incapable of asserting the privilege of combatant immunity that is derived from such a status. As a result, the non-state “warrior” is liable for any domestic law crime resulting from his conduct in battle. Any valid assertion of domestic jurisdiction could reach such an individual. But this does not necessarily mean that the individual has violated the laws and customs of war simply by participating in a non-international armed conflict.
I am not aware of any case involving a conviction for violating the laws and customs of war based on a charge of merely participating in a non-international armed conflict. The law of war violations alleged against non-state actors in such conflicts have been based not on mere participation, but on acts that violated specific law of war rules (like common article 3). In addition, such individuals have routinely been prosecuted for their actions that did not violate the laws and customs of war, but did violate domestic law. But again, subjecting such an individual to prosecution for violating domestic law is a result of the lack of combatant immunity, and not an indication the participation in the conflict was an independent war crime.
Perhaps I am overlooking precedent, but it seems to me that simply extending the “unlawful belligerent” precedents from the context of international armed conflict to non-international armed conflicts does not sufficiently validate this offense. I question whether lack of status as a lawful belligerent in a conflict where it is impossible to be a lawful belligerent is itself an offense in violation of international law, as opposed to just a status that prohibits an assertion of immunity from domestic criminal jurisdiction.