It seems to me that Arabisation stands out as being an unbelievably successful cultural movement. After the Arab conquests, many peoples with distinct cultures and religions were folded into a single identity.
I understand that there is a massive amount of diversity within the group of peoples that identify as Arabs. The people of Egypt still have largely ancient Egyptian ancestry, some "black" Somalians are considered Arab, and even Maronite Christians in Lebanon. But that's what makes this even more strange to me.
The identity is and isn't tied to Islam and is and isn't tied to having actual Arab ancestry. It reminds me of a kind of civic national identity, eg Roman. The difference, in this case, is that even after the fall of the Abbasid/Umayyad caliphates, the identity persisted.
Since then, the "Arab" nations have been disunited and under the rule of many local and foreign powers and yet Arabisation has continued to this day. Pan-Arabism has shown how important this identity is, sometimes superseding national identity.
So to summarise, my questions are:
Why were so many conquered peoples keen to adopt the Arab identity, to begin with (despite not being Arabs or Muslims in some cases).
What made this identity important to hold on to for both the peoples and the rulers that inhabited the post-caliphate emirates and sultanates. Especially as you might think it useful to cultivate a more local identity (from the ruler's point of view, as happened after the collapse of other similar empires).
What is the explanation for the exceptions? For example, most Berbers were Arabised, others weren't and why are the Maronites Arabs and the Copts not?
The answer is very simple actually, just like China the Arab caliphates slowly tried to assimilate those other cultures into their culture. Remind you that those regions in North Africa were very unstable, the Vandals had raided those regions repeatedly after the fall of the Western Roman Empire, even though Justinian Retake those lands from the Vandals, the administration still wasn't very stable because the Byzantine Empire was busy with their rivalry with Persia so they hardly paid attention to North Africa. Now, out of North Africa, the regions in Mesopotamia were tired of the constant wars between Rome and Persia so they were eager to find a new power to serve who could end this conflict and stabilise their region, so the Arabs easily cooperated with them while conquering the Byzantine and the Persian empires. Once they conquered them, they assimilated them to their culture and they were able to do it pretty easily because they suffered from religious wars too, and the concept of one God inspired them.
The Arab and the Chinese Civilisation were very good at assimilating other cultures.