Islam
Bakr, who was Muhammad's intimate friend and collaborator. Others added their support and
Abu Bakr was made the first caliph. This choice was disputed by some of Muhammad's
companions, who held that Ali ibn Abi Talib, his cousin and soninlaw, had been designated
his successor. Abu Bakr's immediate task was to avenge a recent defeat by Byzantine (or
Eastern Roman Empire) forces, although he first had to put down a rebellion by Arab tribes in
an episode known as the Ridda wars, or "Wars of Apostasy".
The territory of the Caliphate in 750His death in 634 resulted in the succession of Umar as
the caliph, followed by Uthman ibn alAffan and Ali ibn Abi Talib. These four are known as al
khulaf' arrshidn ("Rightly Guided Caliphs"). Under them, the territory under Muslim rule
expanded deeply into Persian and Byzantine territories.
When Umar was assassinated in 644, the election of Uthman as successor was met with
increasing opposition
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