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This part seems to be the basis of the US saying it is not bound by the convention.
"Although one of the Powers in conflict may not be a party to the present Convention, the Powers who are parties thereto shall remain bound by it in their mutual relations. They shall furthermore be bound by the Convention in relation to the said Power, ,b>if the latter accepts and applies the provisions thereof."
One could argue that since Al Q'aeda does not seem to acccept or implement the convention, then the US is not bound by it either. That's their argument isn't it?