To what extent did religious divisions cause the decline of the ‘Abbasid Empire?

The question requires that candidates consider the merits or otherwise of the suggestion that religious divisions caused the decline of the ‘Abbasid Empire. Candidates may refer to powerful opposition from Islamic rivals such as the Fatimids and the Umayyads in Spain who controlled large territories and challenged the Empire. Other religious groups such as the Carmathians, Assassins, Almoravids and Seljuks caused disunity and internal conflicts. Other factors may include the size and cultural complexity of the Empire which made administration and unity difficult, financial mismanagement by the central government led to the surrender of central power to local rulers for financial considerations. Numerous invasions by groups such as the Seljuks, Crusaders, and the Mongols greatly weakened the Empire. Weak leadership and internal divisions in the central government contributed significantly to the decline in imperial power. Candidates' opinions or conclusions will be presented clearly and supported by appropriate evidence.