Which nations vied for power in the Arab Caliphate in 750? Why did the Arabs not play a leading role in this?

The Syrians and Arab townspeople defended the former dynasty of the Omaivd caliphs. The Arabs living in the desert (Bedouins) supported the new dynasty of the Caliphs of the Alids (Fatimids), but to no avail: their economy could not stand the competition with Syria and Iran. The Persians and other eastern peoples of the caliphate supported the dynasty of the Abbasid caliphs and won.

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