The Shiites (or Shi'ites or Shia) is the more radical branch of Islam. A schism in Islam occurred in A.D. 660 after Muhammad had died. The Sunnis, the largest group, disagreed with the Shiites over who should be the successor to Muhammad.
To this day, the Sunnis and Shiites clash with each other, with the Sunnis considered to be more moderate and friendlier to western countries like the United States and the Shiites viewed as more extreme and hostile to western countries. The Sunnis are Arab and have ruled countries such as Saudi Arabia and Iraq, while the Shiites have majorities in Iraq and Iran.