Most people who believe in the Doctrine of the Trinity claim that at the Council of Nicaea in 325 AD, all the church did was to officially declare a doctrine that had always been the teaching of the church. But if this is true, ask yourself why? Why would the church have to make any kind of official declaration about a doctrine that was supposed to be established from the beginning? There is no doctrine on whether Jesus resurrected or not. It was an established teaching. The idea that Jesus was God, was not. This is why the church required an official declaration to formally establish this as orthodox. It was a developing idea. It was not a teaching of the early church that had been established by the apostles. An important thing to note in support of this fact is that even at Nicaea when with Emperor Constantine’s help, they rammed this doctrine through as orthodox, they did not include the Holy Spirit as part of the formula. Again, why not? How could they forget that the trinity included the Holy Spirit? Because it was a developing idea, and at this point in time (Nicaea), all the church was willing to concede to was a binity. It would have to wait until the Council of Constantinople in 381 AD to include the Holy Spirit in their formula and thus complete the trinity.
An excellent proof that the Doctrine of the Trinity was not an established teaching of the early Christians is in a letter by one of the trinity’s greatest exponents, Tertullian of Carthage. Even though his understanding of it was that the Son was subordinate to the Father, which is contrary to today’s Doctrine of the Trinity, his writings were unfortunately, very influential in the development of this doctrine. He wrote about it profusely.
The fact that he believed the Son to be inferior to the Father can be easily seen in his letter Against Praxeas. In it, he states:
Chap. IX. "Thus the Father is distinct from the Son, being greater than the Son."
Chap. VII. "And while I recognize the Son, I assert his distinction as second to the Father."
Again, ask yourself why was his view of the trinity different from today’s view if it has always been taught by the church? The reason is because it was a developing idea.
Tertullian himself gives us the greatest proof of the fact that it was a developing idea in the same letter. He states: Chap. III. vv. 1. "The majority of believers, are STARTLED at the Dispensation (of the Three in One)...They are constantly throwing out against us that we are preachers of two gods and three gods...While the Greeks actually REFUSE to understand the oikonomia, or Dispensation" (of the Three in One).
These are incredible statements! Tertullian is acknowledging that the majority of believers did not agree with the Doctrine of the Trinity. They accused him of being a polytheist. The Greeks (either Greek Christians or Christians that spoke Greek in different lands) refused altogether to believe him. These statements are probably the best proofs that the Doctrine of the Trinity was not taught by the Apostles. If it had been taught by them, the majority of believers would have known about the Dispensation and would not have been startled by it, neither would they have accused him of worshipping two gods. This doctrine was something new, it was not the established belief of Christianity as you can see. It was starting to work itself out and trying to gain popularity, especially with Hellenized Christians. But it was not in the majority. In fact, it was very much in the minority.
Now back to the subject of Nicaea. For those that think that Nicaea just formalized an already established teaching, think again. Let us now look to the events that followed after the Council of Nicaea. It will shed some light on the matter.
A BRIEF HISTORY OF THE CHURCH AFTER NICAEA
325 AD - Constantine convenes the Council of Nicaea in order to develop a statement of faith that can unify the church. The Nicene Creed is written, declaring that "the Father and the Son are of the same substance" (homoousios). Emperor Constantine who was also the high priest of the pagan religion of the Unconquered Sun presided over this council. According to the Encyclopedia Britannica:
"Constantine himself presided, actively guiding the discussions and personally proposed the crucial formula expressing the relationship of Christ to God in the creed issued by the council. "of one substance with the Father."
The American Academic Encyclopedia states:
"Although this was not Constantine’s first attempt to reconcile factions in Christianity, it was the first time he had used the imperial office to IMPOSE a settlement." At the end of this council, Constantine sided with Athanasius over Arius and exiled Arius to Illyria.
328 AD - Athanasius becomes bishop of Alexandria.
328 AD - Constantine recalls Arius from Illyria.
335 AD - Constantine now sides with Arius and exiles Athanasius to Trier.
337 AD - A new emperor, Contantius, orders the return of Athanasius to Alexandria.
339 AD - Athanasius flees Alexandria in anticipation of being expelled.
341 AD - Two councils are held in Antioch this year. During this council, the First, Second, and Third Arian Confessions are written, thereby beginning the attempt to produce a formal doctrine of faith to oppose the Nicene Creed.
343 AD - At the Council of Sardica, Eastern Bishops demand the removal of Athanasius.
346 AD - Athanasius is restored to Alexandria.
351 AD - A second anti - Nicene council is held in Sirmium.
353 AD - A council is held at Aries during Autumn that is directed against Athanasius.
355 AD - A council is held in Milan. Athanasius is again condemned.
356 AD - Athanasius is deposed on February 8th, beginning his third exile.
357 AD - Third Council of Sirmium is convened. Both homoousios and homoiousios are avoided as unbiblical, and it is agreed that the Father is greater than His subordinate Son.
359 AD - The Synod of Seleucia is held which affirms that Christ is "like the Father," It does not however, specify how the Son is like the Father.
361 AD - A council is held in Antioch to affirm Arius’ positions.
380 AD - Emperor Theodosius the Great declares Christianity the official state religion of the empire.
381 AD - The First Council of Constantinople is held to review the controversy since Nicaea. Emperor Theodosius the Great establishes the creed of Nicaea as the standard for his realm. The Nicene Creed is re-evaluated and accepted with the addition of clauses on the Holy Spirit and other matters.
If you believe that Nicaea just formalized the prevalent teaching of the church, then there really should not have been any more conflicts. Why should there be? If it were the established teaching of the church, then you would expect people to either accept it, or not be Christians.
It was mainly a theological power grab by certain factions of the church. The major complication throughout all this was that the emperors were involved. At Nicaea it was Constantine that decided the outcome. Then as you can see, we have the flip-flopping of opinion with the result that Athanasius is exiled and recalled depending on which emperor is in power. We even have in 357 AD the declaration that homoousios and homoiousios are unbiblical, and that the Father is greater than His subordinate Son. This is 180 degrees from Nicaea. It is definitely not the Trinitarian formula.
In 380 AD Emperor Thedosius declared Christianity to be the state religion. One can come to the conclusion that whichever way Theodosius favors, is the way in which it is going to end. This is exactly what happened next. In 381 AD the struggle was finally ended by the current emperor, Theodosius the Great, who favored the Nicene position. Just like at Nicaea, the EMPEROR again decided it. What is plainly obvious is that the emperors were dictating the theology of the church. The big difference now being was that there was not going to be any more changing of sides. It was now the state religion. You cannot make Christianity the state religion and then change its beliefs every few years, it would undermine its credibility as the true faith. The Trinity was now the orthodox position, and the state was willing to back it up. Yet, Conflicts and debates continued for centuries.
In 529 AD Emperor Justinian revamped the Roman Civil Law and heresy was big on his list of crimes. The two heresies that were now punishable by death were not accepting the Nicene Creed and rebaptism. It is quite interesting.
I have given historical dates and documents that are recorded in time... not opinion! As taken from the works of J Baixeras

Paul