From Syria to Yemen, the fierce rivalry between Sunni Saudi Arabia and Shiite Iran is heightening regional sectarian tensions, even in conflicts that analysts say are primarily political. Riyadh and Tehran adhere to different branches of Islam and have often backed adherents to their own sect in regional conflicts. The differences between Islam's two main branches -- Sunni and Shiite -- date back to a long and bloody leadership dispute after the death, in 632, of the founder of Islam, the Prophet Mohammed.VIDEOGRAPHIC
