Question

Why did the Abbasids claim that they were the rightful heirs to the caliphate? ​

Answer 1

Answer:

The Abbasids, descendants of an uncle of Muhammad, owed the success of their revolt in large part to their appeal to various pietistic, extremist, or merely disgruntled groups and in particular to the aid of the Shiʿah, who held that the Caliphate belonged by right to the descendants of ʿAlī.The Abbasids, who ruled from Baghdad, had an unbroken line of caliphs for over three centuries, consolidating Islamic rule and cultivating great intellectual and cultural developments in the Middle East in the Golden Age of Islam.

Explanation:

this is the answer to your question