What are some reasons why the Sunnis and Shiites don't get along?

Answer 1

Since both Sunnis and Shiites are Muslim, most of their doctrine is identical; the two sects diverge on the question of how the successor of the prophet (after his death) should be chosen. In most cases, Sunni and Shiites get along, just as most of the world's people get along, regardless of religious differences. A parallel to Christianity might be the differences between Catholics and Anglicans: a single doctrinal difference centuries ago has created two distinct groups who agree on most things.

Much of the conflict between Shiites and Sunni can be explained by other means, such as the rivalry between Southeast Asian powers who happen to be of different sects, for example the Arab Gulf states (who happen to be largely run by Sunnis) have a longstanding rivalry with Persian Iran (which happens to be largely run by Shia) over resources and influence.

As far as the original divide goes, Sunnis supported the election of a Caliph to succeed the Prophet, while Shia believe that Mohammad named a successor, who should have become the rightful Caliph:

Muslims elected Abou Bakr to be the first Caliph after prophet Muhammad (PBUH) death. However, some Muslims believed that the successor should be from the family of the prophet and hence should Ali Ibn Abou Taleb (the prophet cousin and husband of his daughter). However, after the election of AbouBakr, they joined the majority and even Ali Ibn Abou Taleb (God be pleased with him) supported the elected Caliph. The same scenario was repeated after election of Omar Ibn Alkhattab as the second Caliph and Othman Ibn Affan as the third Caliph. Ali Ibn Abou Taleb was then elected as the fourth Caliph.