Yup, Afghanistan a bad example at that point - I was thinking too far ahead there!
And, yes, Afghanistan does unite against foreign invaders but seems to get loose at the seams when there is no external threat. This
gives an idea of the problems there - the north of the country always seems to have been the area of least united tribal and regional groups, the most local warlords who all want their share in the booty. The Taliban were the strongest group during the Russian occupation, with the help of the West of course, but their "remit" was mainly in the south. Are we going to repeat this in Syria I wonder?
Saudi Arabia was only united, under Grand Sherrif then King Hussein, during WW1 (with the help of T. E. Lawrence) in opposition to the Ottoman Empire. Before that there was a lot of internal fighting between the traditional factions and tribes. The smaller states were more united in themselves but it was probably the British influence and WW1 that showed them that inter state fighting was not helping any of them - the fact that they, or at least their ruling families, were all "united" by being of the Sunni sect helped. IIRC there was still a degree of intra-family intrigue even after the war.
My deepest interest in this goes back about thirty years but I try to keep abreast casually. Not sure if, in basics, a lot has changed since then . . .
Whatever, if it involves any nation from Turkey to Afghanistan they share a large degree of similarity of thought and will always possibly be a problem in terms of alliances with the west. If not something in their genes it has become something in their psychology due to a lot of shared history and a shared religion.
The Romans beat or traded some of the inter-tribal aggressiveness out of many European nations and gave the rest a model to build on - probably their lasting heritage to us and far more important than all the ruins!
"Look forward; yesterday was a lesson, if you did not learn from it you wasted it."