Among Muslims
Sectarian violence between the two major sects of Islam, Shia and Sunni, has occurred in countries like Pakistan, Iraq, Afghanistan, Bahrain, Lebanon etc. This violent conflict has roots in the political turmoil arising out of differences over the succession to Muhammad. Abu Bakr, a companion of Muhammad, was nominated by Umar and elected as the first Sunni Rightly Guided Caliph. However another group felt that Ali, the cousin and son-in-law of Muhammad, had been designated by Muhammad and is considered by Shia as the first Imamah.
Abu Bakr was followed by Umar as caliph of the Rashidun Caliphate, then by Uthman ibn Affan and finally by Ali. Ali's right to rule was challenged by Muawiyah bin Abu Sufian, governor of Syria, who believed that Ali should have acted faster against the murderers of Uthman. The situation detoriated further when many of those responsible for the death of Uthman rallied behind Ali. However, later on, both the parties agreed to have some one as a judge between them. This led to the separation of an extremist group known as Kharijites from Ali's army, which pronounced the judgement belonged to God alone. A member of this group later assassinated Ali. At the demise of Muawiyah he appointed his son Yazid as his successor. The credentials of Yazid were challenged by Ali's son Hussein ibn Ali (and grandson of Muhammad). A battle at Karbala in Iraq led to the martyrdom of Hussein and dozens of others from Ahl al-Bayt (the members of the family of Muhammad).
This tragic incident created deep fissures in the Muslim society. The conflict that had started at a political plane intervened with the dogma and belief systems. Those who considered Ali to be the true heir to the Caliphate split away from the main corpus of Muslim society and traditions. They developed their distinct sect, known as "Shia" referring to Shian-e-Ali. The majority of Muslims are known as "Sunni" meaning "followers of the Traditions of The Prophet ". They are of the view that the bloody conflict between Ali and Muawiyah was a result of a tragic misunderstanding and regardless of who was wrong, the matter should have been solved peacefully.
Read more about this topic: Sectarian Violence