Chapter 9 Vocabulary Key Terms Shi?ites Sunnis Sasanid Empire Mecca Muhammad Muslim Islam Medina Umma Caliphate Quran Umayyad Caliphate Abbasid Caliphate Mamluks Ulama Hadith Definitions: Shi?ites- Muslims belonging to the branch of Islam believing that God vests leadership of the community in a descendant of Muhammad?s son in lay, Ali. Shi?ism is the state religion of Iran. Sunnis- Muslims belonging to the branch of Islam believing that the community should select its own leadership. The majority religion in most Islamic countries. Sasanid Empire- Iranian Empire with a capital in Ctesiphon, Mesopotamia. The Sasanid emperor established Zoroastrianism as the state religion. Islamic Arab armies overthrew the empire.