Tribalism is a large part of it. If you read T.E. Lawrence (of Arabia). It was one of his biggest problems. Getting tribal enemies to unite long enough to fight the Turks was a headache for the British. It was also used by Turks as a means of dividing the Arabs who in any case tended not to see themselves as Arab at all.
If you think that's not relevant. Remember this was less than a hundred years ago. A dot in time for many cultures.
Tribalism can be very persistent. In my own country it still exists although mostly in a sporting context. It was the reason we were so easily conquered by the English hundreds of years ago. I can even tell you what tribe I belong to: The Dalcassian. Even the city I live in at the moment is known as the 'City of the Tribes', although those tribes were in fact English families. Even in America, people identify themselves as German, Irish, Hispanic etc. That is a form of tribalism.
I wouldn't underestimate the power of tribalism in the Arab world. I suspect Iraqi is less of a national identity more of a geographical description.