It goes further back than GW1... try WWI.

[Winston Churchill was instrumental in creating Iraq after World War I. The 1921 Cairo Conference, which he convened as Colonial Secretary, set up the British mandate and laid out its boundaries, which encompass three separate peoples‹Kurds, Shiite and Sunni Moslems‹who cordially hate each other. Churchill argued for a separate Kurdistan at the time, where the Kurds would be safe "from some future bully in Iraq." But he was overruled by his own Foreign Office, who were certain that Iraq with its British-installed monarch, King Feisal, would never pose a threat to the Kurds, or to anyone else.]

http://www.winstonchurchill.org/fh97www.htm

Separate states may be the answer for a while. It may even work in the long run.