Ali ruled from 656-661 CE. During this time the
internal tensions in the Muslim community came to a head resulting in a kind of
civil war and political upheaval which ultimately split Muslim allegiances. In 661 Ali, like his two predecessors was assassinated. Muawiya was chosen to succeed him, however, given the split in allegiances, the caliphate of Muawiya and those that followed are not regarded in the same light as the four rightly guided caliphs.
The divisions that surfaced during the time of Ali's caliphate are the basis for the existence of the Shi'ia and Sunni groups in Islam today.