Complex sentence: Shias also believe that Ali was the first Caliph and successor to Prophet Muhammad (SAW), while Sunnis believe that Abu Bakr, Umar, Uthman and Ali were all the four rightly guided caliphs of Islam.
Split into simpler sentences: Shias also believe that Ali was the first Caliph and successor to Prophet Muhammad (SAW). While Sunnis believe that Abu Bakr, Umar, Uthman and Ali were all the four rightly guided caliphs of Islam.