How was the Umma fragmented politically into three distinct centers of power and how did this disunity jeopardize the Islamic dream of a universal community in the Islamic World of the 11th century?

How was the Umma fragmented politically into three distinct centers of power and how did this disunity jeopardize the Islamic dream of a universal community in the Islamic World of the 11th century?
Who are the Mamluks and how did they rise to political power?
How did the Mamluks (the imperial guards) and the viziers (chief administrators) become de-facto rulers of Baghdad, the capital of Abbasid Empire?
How did the emergence of Turkish Mamluk dynasties result in a Persian cultural renaissance?
After the fragmentation of the Abbasid Empire, which Mamluk dynasty controlled most of their former territory? And which battle brought them face to face with the Christian world?
Who were the “Assassins”? What is the origin of the word? why were they considered a cult? And how were they able to create an environment of insecurity in fear in the Umma?