As we close the 4th Century, at least in this aspect (we must remember that Augustine did his fair share of doctrinal development regarding the Trinity) we find that in the end, a young Emperor used the force of Rome to settle the councils and their questions.
The Council asked the Emperor to nominate ‘norm Bishops.’ All bishops had to be in communion with these certain bishops or be driven from their Sees. The Emperor stated that all should follow the religion of Peter
To insure that people would be forced into accepting the trinity, shortly after the 381 council, Emperor Theodosius’ declared:
It is our desire that all the various nations which are subject to our Clemency and Moderation, should continue to the profession of that religion which was delivered to the Romans by the divine Apostle Peter, as it has been preserved by faithful tradition and which is now professed by the Pontiff Damasus and by Peter, Bishop of Alexandria, a man of apostolic holiness. According to the apostolic teaching and the doctrine of the Gospel, let us believe the one deity of the Father, the Son and the Holy Spirit, in equal majesty and in a holy Trinity. We authorize the followers of this law to assume the title of Catholic Christians; but as for the others, since, in our judgment they are foolish madmen, we decree that they shall be branded with the ignominious name of heretics, and shall not presume to give to their conventicles the name of churches. They will suffer in the first place the chastisement of the divine condemnation and in the second the punishment of our authority which in accordance with the will of Heaven shall decide to inflict. (Henry Bettenson, Documents of the Christian Church, Oxford University Press, 1967, 2nd. (1st. 1943), p. 22
So the Trinity needed the force of Roman punishment against non-trinitarians.
Historical scholar Jonathan Roberts wrote:
Until Theodosius commanded his subjects to believe in the doctrine of the Trinity, and enforced his commands upon them by the most inhumane ways, that doctrine was rejected and resisted by the Greek and Roman followers of the Christos…That so senseless and unnatural doctrine should have been forced upon any people, by any means, however tyrannical is a mystery even more mysterious than the arithmetic that can make one three, and three one (Roberts JM. Antiquity Unveiled: Ancient Voices from the Spirit Realms Disclose the Most Startling Revelations, Proving Christianity to be of Heathen Origin …Published by Oriental publishing co., 1894. Original from the University of Michigan, Digitized May 21, 2007, p. 468).
The major questions had been settled. The West called a council in Rome the following year which affirmed the new statement of faith, as well attempted to settle lingering political disputes including the primacy of the Roman Bishop.