He also had many UN nations coming saying "We have proof of WMDs! We have proof! Move in QUICK before he hides them!"
So we went in with a bunch of other countries (who are still there along with us) and we were like okay where are the WMDs and then we found a shit ton of them (declassified document 7/2006 or so with a huge list of non-nuke WMDs found) but didn't find nukes.
Oh, yeah, and then there's the satellite photos of UN inspectors FINALLY being allowed to go inspect the nuclear facilities, driving up and parking out front while chains of flatbed trucks rolled out the back and across the boarder into Turkey.
Pretty much common knowledge, yeah.