Complex sentence: The Fitna began as a series of revolts fought against first Imam of Shia'a and fourth and final of the Sunni Rightly Guided Caliphs Ali ibn Abi Talib, caused by the controversial assassination of his predecessor, Uthman Ibn Affan.
Split into simpler sentences: The Fitna began as a series of revolts fought against Ali ibn Abi Talib, the fourth and final of the Sunni Rightly Guided Caliphs and first Imam of Shia'a. It was caused by the controversial assassination of his predecessor, Uthman Ibn Affan.