Shiism is the name of the smaller of the two major branches of Islam. It developed after the death of the Prophet Muhammad, when his followers split over who would lead Islam. The Shiism branch favored Muhammad’s cousin and son-in-law ‘Ali ibn Abi Talib. Its followers are called Shiites. Use Shiite instead of Shi’ah unless in a quote or as part of a name. Uppercase in all uses.
See Islam, Sunni.
REFERENCE: Religion Stylebook