Why Iraq? Because Saddam had been defying the UN for 12 years and the resolutions had been given plenty of time to work but didn't. Saddam just enriched himself the whole time with deals by corrupt officials. The fact he was willing to invade Kuwait made a lot of people worried what he would do if he got weapons. The first Gulf War was ended on a ceasefire with the condition Saddam certify all weapons programs had been destroyed and dismantled. Saddam never did so the war technically never ended.
There actually is some evidence to support the idea Saddam had wmd's sent to Syria in June 2002. A dam broke in that country at the time and Saddam was very eager to send "humanitarian items."
But you don't have to take my word for it.

http://www.amazon.com/gp/product/1591454042/ref=wl_it_dp/002-4382805-0197647?ie=UTF8&coliid=I7NFQ134XZKMM&colid= 3I07YG19ITNVR

"Saddam's Secrets" by Iraqi general Georges Sada