What was the mistake of the Iraq War? Was it WMD?
No. The statements made by Pres. G.W. Bush and Tony Blair were essentially correct. They said that Iraq had previous WMD programs and had not fully complied with inspections. The war discovered WMDs that were more or less consistent with what had been alleged. This is all well-documented, and you can read about it on Wikipedia.
No, the WMD was just a sideshow. The problem was that there was no cost-benefit analysis justifying the war the war cost us trillions of dollars, and there was never any hope of obtaining commensurate benefits.
I see a similar mistake with the Wuhan virus today. The govt policy is costing trillions of dollars. While it is postponing some deaths, there may be no net saving of lives when it is all over. It is quite possibly the most destructive govt policy since World War II.