Well since I do have an advanced law degree in International Law, I might as well try answer this question raised by Donald at Crescat that Sandefur references relating to whether what Saddam did when he attacked Kuwait really violated any international law. Donald writes (Sandefur's ellipses):
at the time of the invasion of Kuwait, Saddam was in lawful control of the military...[and] no law existed at that time barring the use of the armed forces in any action that Saddam would have deemed necessary…. But does anyone seriously believe that in the late 1980s or early 1990s a law existed prohibiting violation of the “laws of nations?”
Yes, both natural and positive law existed at the time that made Iraq’s (Saddam’s) actions illegal.
As to the positive law that Iraq (Hussein) violated by attacking Kuwait, Article 2, section 4 of the United Nation’s Charter states that “All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state….” Nations who joined the UN did so by agreeing to the treaty obligations of the UN Charter. Iraq was a member of the UN at the time of the attack.
Now positive international law is basically treaty law—you acquire the international obligation by agreeing to the treaty. If you don’t want the obligation, then don’t agree to the treaty.
There is also a natural law basis for prohibiting these actions. In international law parlance, we use the term “customary international law” to refer to laws that all nations must respect, regardless of whether they agreed to the treaty. Customary international law is of course derived from natural law—laws that bind everyone everywhere. Of course, customary/natural law is a very contentious subject. Very strict “positivists” (often conservatives) want to deny that it exists, or otherwise want to limit it existence as narrowly as possible (for instance Robert Bork recognizes the existence of customary international law—or rather I should say he recognized that our federal courts have the ability to apply such law—but wants it frozen in time as to exactly what our framers thought of such law when the constitution was written. Then, only a few things were recognized to violate international custom—like piracy on the high seas).
But it is well established that an unprovoked armed attack violates customary international law. That is, even if an international state is not a member of the UN or agreed in a treaty that they would refrain from armed attacks, they are prohibited from doing so nonetheless.
Note: I realize that Donald's critique seems to focus on the ability of an Iraqi, as opposed to an international tribunal, to try Hussein. In order to thread this needle, the court will have to find a way to justify its jurisdiction to hear cases that violate "the law of nations."
I'd have to look further into Iraq's constitution and other laws as they existed at that time in order to see if they at that time of the attack had jurisdiction to hear such cases. But then again, what Hussein did clearly violated international law as it existed at that time. Why shouldn't this Iraqi court be able to apply international law? That is, there is nothing special about international law that demands that a cohort of nations acting under the auspices of the "International Community" have the exclusive right to hear such cases. Even if the authority of these Iraqi courts to hear cases that violate the law of nations is newly granted, that is, it didn't exist under domestic Iraqi law at the time of the attack, I don't think it would qualify as an expost facto law, because the norms themselves, and hence Iraq's violation of them, clearly existed at the time of Iraq's action.
Is there really a difference between this Iraqi tribunal, that exists under a newly created system, and a newly created "ad hoc" tribunal run under the auspices of the international community (which is how it was done in Yugoslavia & Rwanda)?