Are they? Because the Sykes-Picot line separates off Kuwait from Iraq?
'There is no a priori reason to expect them to be unified.' I think that pan-Arab nationalism is precisely a priori to the derived forms of Iraqi and Syrian nationalism, in that Michel Afleq's Ba'athist movement was equally strong in both Syria and Iraq, and anticipated them as part of an Arab nation. It was only with the defeat of the pan-Arabist movement, like Afleq's and Nasser's that national movements based on the current administrative regions became stronger, mostly as a consequence of inter-Arab conflict, itself a morbid symptom of the defeat of pan-Arabism.
By contrast, the European nations had evolved over time as integrated economies, whose division of labour was largely internal, whereas the Arab nations borders reflected these self-same European nations' carve-up of the region. -- James Heartfield The 'Death of the Subject' Explained is available at GBP11.00, plus GBP1.00 p&p from Publications, audacity.org, 8 College Close, Hackney, London, E9 6ER. Make cheques payable to 'Audacity Ltd'