Once the Temple was destroyed in Jerusalem, the body of Christ was no longer rooted upon its Jewish foundation and had become separated from her mother. Christianity had found itself dispersed throughout a pagan world, chiefly the Roman Empire. The ancient church of Rome had become the new center of Christianity along with Antioch and Alexandria. The church, once having battled the Jews, now found a new battle, a continual distortion of the Christian faith by various religions and the new Gentile converts of the nations.
The doctrine of the Trinity, as we have it today, was a development that gradually began to emerge as a sectarian reaction between alternate viewpoints of God. The chief catalysts were the Monarchians, especially Modalists (Sabellians). We can see in the writings of the fathers an attempt to explain the relationship of the Father, Son and Holy Spirit as a concerted effort to respond to the teachings of the Modalists. Indeed, the Arian controversy that lasted 60 years in the fourth century, began when Arius thought his colleague Alexander was teaching a view of God which was tantamount to Sabellianism. Arius was not a man bent on teaching deviant ideas. He was a man who was very concerned about the theological developments which were taking place. Whether he was right or wrong is not the issue in matters of history. We must understand that we need to presume his heart concerning the matter was motivated by a righteous zealousness just as much as Athanasisus or anyone else. Had we known him, we may have found him to be a holier man than Athanasius and imaginary histories will not change our surprise on judgment day. The opinions of his opponents concerning his character are not much value since it was fashionable at that time for church leaders to paint their opponents as black as possible, much like politicians do today. It is far too easy to think Arius was out to "attack the Trinity." He did no such thing. The doctrine of the Trinity had not yet been developed and accepted by the church and this was the very reason the opportunity for the confusion was afforded and the dispute erupted.
Modalists taught that God was one person. Objectors to modalism recognized that the Father and the Son were distinct persons. During these disputes, the Holy Spirit was, more or less, left out of the picture, and the controversy focused on the relationship between the Father and the Son. For example, the Council of Nicea did not declare the Holy Spirit was also of the same substance of the Father as it did concerning the Son. All parties strived to preserve the oneness of God while attempting to explain the various revelations in their hands from the Scriptures. Around the end of the second century, certain forms of "Monarchianism" began to emerge and it is here in reaction to these teachings that we begin to see how the Trinity developed as a means to explain God in the the face of perceived heresy.
Various views of God created intense rivalries in the church. Hippolytus became extremely bitter against the two successive Bishops of Rome, Zephyrinus and Callistus, whom he regarded as monarchians and henceforth made himself Bishop of Rome upon Zephyrinus' death and Callistus' ordination. These theological rivalries created a bitter atomosphere and a breeding ground for men to jealously maintain or attempt to seize ecclesiastical control.
There are some Trinitarian apologists who actually have the audacity to claim the doctrine of the Trinity was not developed over time but was simply defended when the occasion called for its defense. This is patently false and many Trinitarian church historians will themselves admit it. If indeed, the Trinity had been an apostolic tradition, these matters would have been settled short and fast by this simple fact alone. And contrary to popular belief, Nicea did not prescribe a doctrine of the Trinity. The doctrine of the Trinity was developed much later by the hands of an aging Athanasius, the Cappadocians, and then by Augustine in the early fifth century. We will here show how the doctrine of the Trinity was developed and not a teaching handed down by the Apostles.