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The Roman Empire officially adopted Nicene Christianity as its state religion in 380 CE through the Edict of Thessalonica, issued by Emperors Theodosius I, Gratian, and Valentinian II. Despite this imperial recognition, the church soon experienced significant fragmentation driven by both political and doctrinal disputes. Early separations included the Church of the East in 424 and the independence of Oriental Orthodox Churches after rejecting the Council of Chalcedon in 451. The fall of the Western Roman Empire in 476 further exacerbated a growing divide between Eastern and Western Christianity, ultimately culminating in the Great Schism of 1054, which formally separated the Latin Catholic Church from the Greek Orthodox Church. Emperors like Constantine the Great and Justinian I attempted to define orthodoxy and maintain unity through councils and imperial control. However, theological rifts, such as Arianism and Nestorianism, and the transformative impact of 7th-9th century Muslim conquests profoundly shaped the trajectory and geographical reach of Christianity.