By that logic...
ALL cease fire agreements fall under that category of "under duress." I don't think that's going to fly very far as a legal precedent.
Raoul points out that the inspectors after the Gulf War found lots of stuff. They would not have been able to do so if we had not fought the war first and eliminated the Iraqi resistance. I dare say that after the next defeat of Iraq, inspectors will also find a lot more stuff than they are finding now.