SHIA: The second largest branch of Islam, accounting for about 15% of the world’s Muslims and the majority of Muslims in Iran, Iraq, Azerbaijan, and Bahrain. About 85% of Shia are Twelver Shia, who believe that twelve divinely ordained and infallible leaders in the family of Muhammad were the Prophet’s successors and the correct source of understanding of his teachings.

Shia holds that leadership can be inherited only by those with the bloodline of the prophet Muhammad.

Where temporal authority derives from religious authority, assigning religious authority is a matter of supreme temporal importance. As far as the two sects are concerned, only one can be right.

Iraq’s population is 55% to 65% Shia, but it was ruled for decades by a secular Sunni government of Ba’athist Arab nationalists until the American overthrow of Saddam Hussein. Iran, to the east, is at least 90%

Shia and aggressively seeks to expand its influence into majority-Shia Iraq. Iraq’s northwestern neighbor Syria is overwhelmingly Sunni but is ruled by a secular Shia Ba’ath party that bitterly opposed the Sunni Ba’athists in Iraq.