Saudi Arabia’s execution of the Shiite cleric Sheikh Nimr al-Nimr could escalate tensions in the Muslim world even further. In the Shiite theocracy Iran, the supreme leader, Ayatollah Ali Khamenei, said on Sunday that Saudi Arabia, which is ruled by a Sunni monarchy, would face “divine vengeance” for the killing of the outspoken cleric, which was part of a mass execution of 47 men. Sheikh Nimr had advocated for greater political rights for Shiites in Saudi Arabia and surrounding countries. Saudi Arabia had accused him of inciting violence against the state.
Here is a primer on the basic differences between Sunni and Shia Islam.