Creating the reasons for war, post-war

Regarding today's Washington Post report that a chemical weapons lab has been discivered in Iraq, James Balkin at Balkinization notes the tragic irony,

In one of the ironies of history, it now turns out that although U.S. troops found no biological and chemical weapons in Iraq when we overthrew Saddam in March 2003, there is evidence that insurgent groups began production of chemical and biological weapons after the invasion to attack U.S. forces there. Thus, we may have inadvertently chosen a policy that led to the production of the very WMD's we fought the war to destroy.