What were the main obstacles of Arab Unity?

What were the main obstacles of Arab Unity?
“What were the main obstacles of Arab Unity?”
Clear effective written skills.
Evidence of analytical understanding, clear argument.
Familiarity of relevant literature.
Suggested sources:
– Pan-Arab Nationalism: The Ideological Dream as Compelling Force Barry Rubin Journal of Contemporary History > Vol. 26, No. 3/4, The Impact of Western Nationalisms: Essays Dedicated to Walter Z. Laqueur on the Occasion of His 70th Birthday (Sep., 1991)
– Khalidi Rashid, The Origins of Arab nationalism , NY Oxford University press, 1991.
– Jankowski, James and Gershoni, Israel (eds.), Rethinking nationalism in the Arab Middle East, New York ; Chichester : Columbia University Press, c1997
-Spencer, P. & H. Wollman, eds (2005) Nations and Nationalism: A Reader (Edinburgh University Press)
– Hobsbawm, E. (1991) Nations and Nationalism since 1780 (Cambridge)