This is a chapter from a scholarly historical and political work — likely written in the early 20th century — surveying the decline of the Abbasid Caliphate and the theory of Islamic sovereignty. The author traces how the Abbasid empire fragmented after its early vigor: provincial governors broke away, Shi'ite dynasties like the Buwayhids reduced the Caliph to a puppet, and the Saljuq Turks briefly offered a chance for a Pope-Emperor-style dualism before the Mongols destroyed Baghdad and the Caliphate in 1258. A distinctive recurring argument is that Arabs are constitutionally incapable of sustaining empire without religious fervor binding them, and that "Muslim civilization" after the first Abbasids was in practice Persian and Turkic, not Arab. The author analyzes the Ottoman claim to the Caliphate — resting on five grounds including conquest, election, and guardianship of Mecca — but argues it is fundamentally undermined by the Prophetic tradition requiring the Caliph to be of the Quraysh tribe. The chapter closes by examining contemporary constitutional implications, including whether Muslims under British rule in India inhabit Dar al-Islam or Dar al-harb, and the spreading custom of praying for the Ottoman Sultan as Caliph in Indian mosques — treating these as live and unresolved political questions at time of writing.