Church history in the context of "Christianity as the Roman state religion"

In the year before the First Council of Constantinople in 381, Nicene Christianity became the official religion of the Roman Empire when Theodosius I, emperor of the East, Gratian, emperor of the West, and Gratian's junior co-ruler Valentinian II issued the Edict of Thessalonica in 380, which recognized the catholic orthodoxy, as defined by the Council of Nicea, as the Roman Empire's state religion. Historians refer to this state-sponsored church using a variety of terms: the catholic church, the orthodox church, the imperial church, the Roman church, or the Byzantine church, with some also used for wider communions extending beyond the Roman Empire. The Eastern Orthodox Church, Oriental Orthodoxy, and the Catholic Church all claim to stand in continuity from the Nicene Christian church to which Theodosius granted recognition. Political differences between the Eastern Roman Empire and the Persian Sassanid Empire led to the separation of the Church of the East in 424. A doctrinal split within the imperial church led to the independence of early Oriental Orthodoxy, while the fall of the Western Roman Empire initiated the gradual separation between Eastern and Western Christianity, culminating in the East-West schism of 1054. The Western Church evolved into the Latin Catholic Church while the Eastern Church that remained under the patronage of the Eastern empire and evolved into the Greek Orthodox Church.

Earlier in the 4th century, following the Diocletianic Persecution of 303–313 and the Donatist controversy that arose in consequence, Constantine the Great had convened councils of bishops to define the orthodoxy of the Christian faith and to expand on earlier Christian councils. A series of ecumenical councils convened by successive Roman emperors met during the 4th and the 5th centuries, but Christianity continued to suffer rifts and schisms surrounding the theological and christological doctrines of Arianism, Nestorianism, Miaphysitism, and Dyophysitism. In the 5th century, the Western Roman Empire decayed as a polity; invaders sacked Rome in 410 and in 455, and Odoacer, an Arian barbarian warlord, forced Romulus Augustus, the last nominal Western Emperor, to abdicate in 476. However, apart from the aforementioned schisms, the church as an institution persisted in communion, if not without tension, between the East and West. In the 6th century, the Byzantine armies of the Byzantine Emperor Justinian I recovered Italy and other regions of the Western Mediterranean shore. The Byzantine Empire soon lost most of these gains, but it held Rome, as part of the Exarchate of Ravenna, until 751, a period known in church history as the Byzantine Papacy. The early Muslim conquests of the 7th–9th centuries would begin a process of converting most of the then-Christian world in the Levant, Middle East, North Africa, regions of Southern Italy and the Iberian Peninsula to Islam, severely restricting the reach both of the Byzantine Empire and of its church. Christian missionary activity directed from the capital of Constantinople did not lead to a lasting expansion of the formal link between the church and the Byzantine emperor, since areas outside the Byzantine Empire's political and military control set up their own distinct churches, as in the case of Bulgaria in 919.

Eusebius of Caesarea (c. AD 260/265 – 30 May AD 339), also known as Eusebius Pamphilius, was a historian of Christianity, exegete, and Christian polemicist from the Roman province of Syria Palaestina. In about AD 314 he became the bishop of Caesarea Maritima.

Together with Pamphilus, Eusebius was a scholar of the biblical canon and is regarded as one of the most learned Christians during late antiquity. He wrote the Demonstrations of the Gospel, Preparations for the Gospel and On Discrepancies between the Gospels, studies of the biblical text. His work Onomasticon is an early geographical lexicon of places in the Holy Land mentioned in the Bible. As "Father of Church History" (not to be confused with the title of Church Father), he produced the Ecclesiastical History, On the Life of Pamphilus, the Chronicle and On the Martyrs. He also produced a biographical work on Constantine the Great, the first Christian Roman emperor, who was Augustus between AD 306 and AD 337.

Nestorianism is a term used in Christian theology and Church history to refer to several mutually related but doctrinally distinct sets of teachings that fall under the umbrella term Dyophysitism, such as two natures in Christ (human and Divine) or two persons in Christ (the Man and the Word). The extent to which those two definitions are actually distinct is also debatable. The first meaning of the term is related to the teachings of Christian theologian Nestorius (d. c. AD 451) as according to his immediate opponents at the Council of Ephesus and traditionally used by Miaphysites. The second meaning of the term relates to a set of later theological teachings that were traditionally labeled as Nestorian by Chalcedonians but differ in the teachings of Nestorius in origin, scope and terminology. Per the latter definition, the Oxford English Dictionary defines Nestorianism as:

The original definition of Nestorianism, as articulated by Nestorius himself, is preserved primarily in his surviving writings on topics such as Mariology and Christology. Although many of his works were lost or destroyed, others have been transmitted through his opponents or preserved in Church of the East libraries. Most notable among these is the Bazaar of Heracleides, composed during his exile following the Council of Chalcedon. The modern rediscovery of the Bazaar has prompted renewed scholarly interest in reconstructing Nestorius’s own theological positions, which appear to diverge in significant respects from the “two‐person” formulation of Christology attributed to him by both his contemporaries and later critics. His theology was influenced by teachings of Theodore of Mopsuestia (d. 428), the most prominent theologian of the Antiochian School. Nestorian Mariology prefers the title Christotokos, which encompasses the term Theotokos ('God-bearer') for Mary, thus emphasizing distinction between divine and human aspects of the Incarnation, and at the same time their unity in the person of Christ. Nestorian Christology promotes the concept of a prosopic union of two concrete realities (divine and human) in Jesus Christ, as opposed to the concept of a hypostatic union of two hypostases into one. The distinction is between 'two hypostases in one person' and 'two hypostases united into one hypostasis', respectively. Hypostasis is not seen as subject, but rather a nature existing in reality. This Christological position is viewed by the West as radical dyophysitism, and, according to Chalcedonian Christianity, differs from their dyophysitism, which was reaffirmed at the Council of Chalcedon in 451. Such teachings brought Nestorius into conflict with other prominent church leaders, most notably Cyril of Alexandria, who issued 12 anathemas against him in 430. Nestorius and his teachings were eventually condemned as heretical at the Council of Ephesus in 431, and again at the Council of Chalcedon in 451. His teachings were considered as heretical not only in Chalcedonian Christianity, but even more so in Oriental Orthodoxy. The Church of the East would affirm the orthodoxy of Nestorius, lining up with the tradition of the School of Antioch of its time.

John Anthony McGuckin (born 1952) is a British theologian, church historian, Orthodox Christian priest and poet.

Catherine Gunsalus González (born 1934) is an American historian, theologian, and ordained Presbyterian minister who is professor emerita of church history at Columbia Theological Seminary in Decatur, Georgia.

Olympiodorus of Thebes (Ancient Greek: Ὀλυμπιόδωρος ὁ Θηβαῖος; born c. 380, fl. c. 412–425 AD) was a Roman historian, poet, philosopher and diplomat of the early fifth century. He produced a History in twenty-two volumes, written in Greek, dedicated to the Emperor Theodosius II, detailing events in the Western Roman Empire between 407 and 425. The history is lost, but much of it is known from its use by other writers.

His friends included philosophers, provincial governors and rhetoricians. He made several journeys in an official capacity, accompanied for twenty years by a parrot. He was a "convinced but discreet" pagan,who flourished in a Christian court, and whose work influenced several subsequent historians, including writers of ecclesiastical history.

First Things (FT) is a journal aimed at "advanc[ing] a religiously informed public philosophy for the ordering of society", focusing on theology, liturgy, history of religion, church history, culture, education, society, politics, literature, book reviews, and poetry. First Things is inter-religious, inter-denominational and ecumenical, especially Christian and Jewish. It articulates Christian ecumenism, Christian–Jewish dialogue, erudite social and political conservatism and a critique of contemporary society.

First Things is published by the New York–based Institute on Religion and Public Life (IRPL) as a monthly, except for bi-monthly issues covering June/July and August/September, and has a circulation of approximately 30,000 copies. First Things' founding editor and editor-in-chief, from 1990 to his death in 2009, was Richard John Neuhaus. Since 2011, R. R. Reno has served as editor.