The laws of war and the scope of detention authority under the AUMF - Part I

As Ben and Jack discuss below, the central issue in al-Bihani II (i.e., the en banc denial) is whether courts adjudicating GTMO habeas petitions should take account of the law of armed conflict ("LOAC" or, if you prefer, international humanitarian law ("IHL") or simply the laws of war) in construing the scope of the President's authority under the September 18, 2001 Authorization for Use of Military Force (or, alternatively, under Article II of the Constitution).  Given the seven votes associated with Chief Judge Sentelle's opinion, the district judges going forward appear free to resolve that issue as they think appropriate, at least until the Circuit has another occasion to weigh in on the matter.  Or more precisely, they are free to resume their ongoing debate regarding what LOAC has to say in this setting.
What are the terms of this debate, and what is really at stake?  Is LOAC even determinate on this point?  I plan to write a number of posts on this issue, as I think it is much harder and more complicated than generally assumed (I've also just completed an article manuscript on the point, and so it was much on my mind even before al Bihani II).
I hope to keep the posts in this particular series bite-sized, and in that spirit will offer only one preliminary thought in this one:
LOAC is not always "on."  Simplifying things a bit, it applies when armed conflict occurs and not otherwise.  Much therefore turns on how one defines "armed conflict," and especially whether one thinks the concept should be strictly limited to geographically-confined circumstances of sustained conventional combat or if instead it can extend to circumstances involving the capture or killing of individuals on an episodic basis in locations (like New York City on 9/11/01) that otherwise appear peaceful.   One can readily imagine the difficulty of drawing lines to cabin the concept, and the diversity of opinion regarding precisely how to draw those lines.  And hopefully one can also appreciate how much of the post-9/11 debate regarding detention turns on this question.  Those who favor a broad approach to the field of application of the "armed conflict" concept will still have to determine both whether the AUMF should be read in light of LOAC and what they think LOAC actually says on the detention scope issue, but they will be less likely to object to the theoretical relevance of LOAC for non-Afghanistan military activity.  Those who take a narrow view of the field of application will not think LOAC relevant at any level, however, at least when it comes to captures outside Afghanistan (that does not mean they think the government has carte blanche, of course; they are likely to raise objections to the use of force and of military detention based on domestic and international human rights laws).
The important point is to appreciate that the al-Bihani debate arises only after one has moved past this threshold dispute.  By and large the GTMO habeas cases have involved captures within Afghanistan, thus largely sidestepping this threshold issue.  Not all of them are like that, however, and thus other complications can and apparently do arise.
In a subsequent post I'll move on to the question of what if anything LOAC truly has to say about the particular categories of persons who can be detained without charge in a context involving clandestine non-state actors that eschew conventional membership structures.