There are several good posts at Opinio Juris about the “legality” of the Iraqi war. For me the issue is rather simple: our constitution has an enumerated power that allows Congress to declare war for whatever reason they choose, and no treaty would change that (it would amount to amending the constitution via treaty).
Being international lawyers, the people at Opinio Juris take a more nuanced view. Julian Ku has a couple of posts (here and here). Chris Borgen responds here.
One point they touch on is the legality of the war in Kosovo. This strikes me as a good point to raise: the Kosovo war was popular among many people that oppose the current war in Iraq and they justify it through a fig leaf of multilateralism via Nato. This seems very dishonest to me, since we’ve heard all of the garbage from the transnationalists that the UN is the only body that can “authorize” war, though they never authorized the actions in Kosovo.
Cassandra has a good, detailed post that explores the hypothetical primacy of international law over domestic law. There’s not much I can add to her post, other than I agree with her and hope that, when the time comes (if ever), it is approached by amending the Constitution, not imposed on us by our robed masters. It would take several decades of goodwill on the part of the rest of the world before I favored this. Even then, I would wait until right before death to say it out loud, so I don’t have to deal with the aftermath.
Cass’s post is a followup to an earlier post of mine. Be sure to wish her well as she takes a little time off from blogging. You’ll have to use a different post for that, as she’s closed comments on the linked post.