> No declaration of war was made on Iraq.

Yes, it was; no special language is needed in a declaration of war; the "Authorization for the Use of Military Force" was plainly and unmistakeably a conditional declaration of war, the conditions for which were fulfilled.

If you declare war, you have to follow Geneva rules, so you can't do Guantanamo detentions; if you do Guantanamo detentions, you're not legally at war. Pick one.

> If you declare war, you have to follow Geneva rules,

The applicability of the Geneva Conventions is affected by the fact of war, but independent of whether there is a declaration. And even if it wasn't, violations of the Conventions would not reach back in time and change whether a declaration had occurred.