Behr (104-119), Ayres (222-243, 260-267)
In 372 Valens travelled to Caesarea and met with Basil. This meeting turned out relatively favourable for Basil, and as a consequence he gained ecclesiastical responsibility for Armenia. Nonetheless, the split of Cappadocia into two provinces threatened his episcopal influence, and he responded by appointing numerous relatives and supporters to newly created sees. During the 370s Basil spends considerable effort in trying to build alliances in the East, deal with the triple-division in Antioch, and approach Rome and the west.
During the 370s, Damasus holds power in Rome, and the correspondence between Basil and Damasus figures significantly in East-West relations. The relationship was strained due to support for differing bishops in Antioch. Nonetheless, Damasus is basically pro-Nicene in his theology.
In 374 Ambrose is elected bishop of Milan. He succeeded the Homoian Auxentius, and seems to be largely unpressured in the early years of his episcopacy.
Valentinian dies in the West, campaigning in Germania, and Gratian succeeds him.
Among other events (infra), Ambrose comes under increasing pressure in Milan, and so writes De Fide, and in a few years adds 3 more books to it, as well as by 381De Spiritu (influence from Didymus, or plagiarism according to Jerome). Ambrose shows familiarity with Eastern pro-Nicene theology, as well as Hilary, and includes elements such as the doctrine of inseparable operations, a sophisticated account of 'generation', and anti-Homoian exegesis.
In 378 the 5th decisive extra-ecclesial event for the 4th century occurs: the battle of Adrianople (the other 4 are: Constantine's unification of Empire, the sole rule of Constantius from 351, the death of Constantius in 361, and the reign of Julian the Apostate). Goth incursions across the Danube led to the defeat of Valens and his army, and Gratian close at hand, in consultation, appointed Theodosius to rule the East. He came out of retirement in Hispania, and was declared Augustus Jan 379. In the same year, Meletius held a small council in Antioch. Ayres sees this as a Basil-Meletius power-bloc become pro-active in moving towards a Nicene settlement, and the council produces a pro-Nicaea statement which it then addresses to Theodosius. This council also sent Gregory of Nazianzus to Constantinople, to pastor the 'Nicene' Christians, a role in which he excelled and gave him the scope for some of the most important oratory of his career.
Behr draws attention to edicts of Theodosius, such as Feb 28, 380, endorsing Nicaea, and the faith of Damasus of Rome and Peter of Alexandria, as a standard for trinitarian orthodoxy. On Nov 24 380, he enters Constantinople, and demands a Nicene confession from Demophilus, who declines and is exiled, this paves the way for Gregory of Nazianzus installation Nov 27.