The split between Shite's and Sunnis began soon after the death of Mohammed.Ê The Sunnis believe that Ali was the last of the rightly guided caliphs ( successors) to Mohammed. The Shiites believe that Ali was the only successor and all future successors should come through his line. The Sunnis do not believe there can be successors to Mohammed.
Today there are important differences between the two major groups in Islam- Those differences are somewhat similar to the differences between Catholics and Protestant in Christianity. The Shia's have supreme religious leaders similar to the Pope who is considered to be a descendant of Ali. The Sunnis do not have one religious leader, instead have distinguished scholars and jurists who issue opinions.
The Shia's glorify Ali and have a strong identification with suffering and martyrdom. On a daily bases the two groups have different calls to prayer, pray somewhat differently.There additional customs that differentiate between the two groups.