When did the fight between oneness believers and triune believers start?

Answer 1

Unfortunately, almost as soon as He left this world...

http://en.wikipedia.org/wiki/Trinitarianism

http://en.wikipedia.org/wiki/Unitarian

Answer 2

--Trinities have been around since ancient Egypt & Babylon.
------: “The origin of the [Trinity] is entirely pagan.”—The Paganism in Our Christianity.

--But as far as the so-called christian establishment 300 yrs after Christ , Please note:

*** ti pp. 7-8 How Did the Trinity Doctrine Develop? ***
AT THIS point you might ask: ‘If the Trinity is not a Biblical teaching, how did it become a doctrine of Christendom?’ Many think that it was formulated at the Council of Nicaea in 325 C.E.
That is not totally correct, however. The Council of Nicaea did assert that Christ was of the same substance as God, which laid the groundwork for later Trinitarian theology. But it did not establish the Trinity, for at that council there was no mention of the holy spirit as the third person of a triune Godhead.

Constantine’s Role at Nicaea

FOR many years, there had been much opposition on Biblical grounds to the developing idea that Jesus was God. To try to solve the dispute, Roman emperor Constantine summoned all bishops to Nicaea. About 300, a fraction of the total, actually attended.

Constantine was not a Christian. Supposedly, he converted later in life, but he was not baptized until he lay dying. Regarding him, Henry Chadwick says in The Early Church: “Constantine, like his father, worshipped the Unconquered Sun; . . . his conversion should not be interpreted as an inward experience of grace . . . It was a military matter. His comprehension of Christian doctrine was never very clear, but he was sure that victory in battle lay in the gift of the God of the Christians.”

What role did this unbaptized emperor play at the Council of Nicaea? The Encyclopædia Britannica relates: “Constantine himself presided, actively guiding the discussions, and personally proposed . . . the crucial formula expressing the relation of Christ to God in the creed issued by the council, ‘of one substance with the Father’ . . . Overawed by the emperor, the bishops, with two exceptions only, signed the creed, many of them much against their inclination.”

Hence, Constantine’s role was crucial. After two months of furious religious debate, this pagan politician intervened and decided in favor of those who said that Jesus was God. But why? Certainly not because of any Biblical conviction. “Constantine had basically no understanding whatsoever of the questions that were being asked in Greek theology,” says A Short History of Christian Doctrine. What he did understand was that religious division was a threat to his empire, and he wanted to solidify his domain.

None of the bishops at Nicaea promoted a Trinity, however. They decided only the nature of Jesus but not the role of the holy spirit. If a Trinity had been a clear Bible truth, should they not have proposed it at that time?............
....
The Athanasian Creed

THE Trinity was defined more fully in the Athanasian Creed. Athanasius was a clergyman who supported Constantine at Nicaea. The creed that bears his name declares: “We worship one God in Trinity . . . The Father is God, the Son is God, and the Holy Ghost is God; and yet they are not three gods, but one God.”

Well-informed scholars agree, however, that Athanasius did not compose this creed. The New Encyclopædia Britannica comments: “The creed was unknown to the Eastern Church until the 12th century. Since the 17th century, scholars have generally agreed that the Athanasian Creed was not written by Athanasius (died 373) but was probably composed in southern France during the 5th century. . . . The creed’s influence seems to have been primarily in southern France and Spain in the 6th and 7th centuries. It was used in the liturgy of the church in Germany in the 9th century and somewhat later in Rome.”

So it took centuries from the time of Christ for the Trinity to become widely accepted in Christendom. And in all of this, what guided the decisions? Was it the Word of God, or was it clerical and political considerations? In Origin and Evolution of Religion, E. W. Hopkins answers: “The final orthodox definition of the trinity was largely a matter of church politics.”

Answer 3

its been going on since the concept of the trinity was invented.