How did shi'a and sunni groups arise?

Answer 1

The major difference is historical. The Shiites did not agree on the elected Caliphs (who followed Prophet Muhammad after his death). They believed that the Caliphs should only be within Prophet Muhammad descendants and family. Accordingly, they were supporting Ali Ibn about Taleb (Prophet cousin and the husband of his daughter Fatima) to be the first Caliph. However, they didn't protest against the elected Caliphs (Abou Bakr, Omar, and Ottman) and even Ali, himself, was good supporter and adviser to the three Caliphs until he was elected as the fourth Caliph.

However, Both Sunnis and Shiites believe that no God except one and only one God, the Creator with no partner, no father, no son, no companion, no associate, and no resemblance and that prophet Muhammad is His messenger and prophet. They both believe in God Angels, all God prophets, all God holy book, the Day of Judgment, and destiny. They believe in the five Pillars of Islam. They both face the direction of Kaaba when praying. They pray in any mosque regardless the praying leader is Sunni or Shiite. They may differ in some minor details of rituals but these details are not critical to neither the Shiites nor the Sunnis.