History of The Doctrine Concerning The Nature of God In The Early Centuries of Christianity
Anti-Trinitarians In The Later Christian Centuries
Michael Servetus (1511-1553), a scholar, physician, and scientist of note; deeply religious and devoted to Christ, wishing to restore what he called true Christianity, would not conform to the accepted doctrine of the trinity. He also denounced predestination and infant baptism. He was arrested, presumably at Calvin’s insistence. Servetus was condemned on the charge that he denied the trinity and rejected infant baptism, offenses punishable by death under the Justinian code.  (Luther and Calvin consented to his death). In spite of Calvin’s plea for a more merciful form of execution, Servetus was burned at the stake. Henceforth, Calvin’s position in Geneva was not to be seriously contested.  (the reformed church later put up a monument, repenting).
(Trinitarians are usually quite silent about such things — the reformers, being classed as heretics for dissenting from the roman catholic church and being hunted down and murdered — should have been sympathetic to those, who in all good conscience, differ from them).
Some who found refuge at Geneva sympathized with Servetus, and to the distress of Calvin, tended toward anti-Trinitarians. Similar trends disturbed the reformed churches in Bern and Zurich. Anti-Trinitarians had a marked development in Poland, called Socinianism from lelio sozini who was courtly in manner, modest, deeply religious, of irreproachable morals. His spiritual pilgrimage never led him to a formal break with the Swiss and Geneva reformers. However, he deplored the burning of Servetus.
Others of the reformation were inclined to be anti-Trinitarians. Some of the Italian Anabaptists (those who rebaptized after conversion people who were sprinkled while infants) began to develop anti-Trinitarian convictions and multiplied having congregations and pastors, and holding a council in Venice in 1550.
Another center of anti-Trinitarian views was in the Grisons, a republic between Italy and Switzerland. In 1553 the synod of the Grisons attempted to impose a Trinitarian faith; by 1575 anti-Trinitarian ministers had been largely rooted out.
In Transylvania, an anti-Trinitarian form of Protestantism was making rapid progress. In Poland (in the end of the 15th c.) The reformed churches were anti-Trinitarians, to which Socinus gave leadership (called Socinian’s). The Socinian’s had opportunity in Russia and the Ukraine. Many others had similar views, including the remonstrant and some of the Mennonites in Holland. In 1659 the Socinian’s were banished from Poland by decree of the diet. The anti-Trinitarian’s chief gains on the continent were among the reformed; in England it was from the Presbyterians; in the u.s.a. from the puritans.
In the 1780’s the oldest congregation in the church of England, in new England, officially abandoned belief in the trinity.  (some of these anti-Trinitarians held moralistic monarchial views, some dynamic monarchian views, and others the modern unitarian views of a completely human Christ.) For example, in 1815 e. Channing became an exponent of arian views and he accepted the name unitarian for the movement. (the term “unitarian” had been applied earlier to the szklers in transylvania and to others, even those believing in the deity of Christ).  the campellites or disciples of christ of the 1800’s were an undenominational fellowship of devout christians who were anti-trinitarian but who believed in the deity of jesus.
Congregationalists were deeply stirred by the great awakening which began in 1790 and some of the clergy as well as the laity were affected by Armenians and Socinianism. Some of the general Baptist moved in that direction, as did a new anglican clergymen. 
(nor was the oneness doctrine confined to the late middle ages; in 1115 a.d., abelard canon of notre dame was charged with sabellianism.  he was possessed of a rapier-like intellect, was charming, keen, a stimulating teacher; a sincere Christian. He went to various centers, in some places, worsting his teachers, and eventually became the most popular of the lecturers in paris. Abelard antagonized many. His enemies had him hailed before the council at soissons in 1211 for heresy. In 1140 he was condemned by a council at sins because his views on the trinity and other subjects were regarded as subversive to the faith. 
About the time of World War 1, a doctrinal controversy swept through the heartland of the united states. The “new issue”, oneness, contended that true baptism must be “in the name of Jesus” only, rather than employing the traditional formula. Furthermore, the proponents of this view denied that there are three persons in the godhead. For a time, this teaching threatened to topple the assemblies of god, because many of its leaders — men like h.g.rodgers, eudorus n. Bell, howard a. Goss, and Daniel c. O. Opperman –submitted themselves for rebaptism in “Jesus’ name.” the ministerial roll of the assemblies of god was decreased by more than 150. Its general council inst. Louis (1916) prepared a “statement of fundamental truths.” the right to draft such a statement was challenged by the “oneness” contingent on the grounds that the formative scriptures were to be the “all-sufficient rule for faith and practice,” and here was a man made creed being proposed. They argued that this was a departure from the liberty which had characterized earlier Pentecostalism. The assemblies of god withstood the challenge and articulated a position that was staunchly Trinitarian. Men like j. Roswell flower and john w. Welch remained staunchly Trinitarian, criticizing the new revelation on the ground that it was too dependent upon the subjective feelings of the individual and not enough on theological> principles. 156 ministers withdrew from the assemblies of god, and a new Pentecostal body was organized — the Pentecostal assemblies of the world. 
The United Pentecostal Church is the largest “oneness” group of Pentecostals. In 1965 it numbered 200,000 (spirit filled, adult) members. 
(many times a division, or split, develops when one preaches the truths of god’s word that are in opposition to that of the established church teachings.in such cases, those who reject the truth of the bible, substituting instead the traditions of men, would be held accountable for the division in the church — not those who are faithful and bold enough to reinstate the truths of scripture.) For example, it was the Jews that refused the truth that Jesus was the messiah, that were to blame for the split in the synagogues that Paul preached in, not paul — they should have accepted it! The same holds true, to a lesser degree, between the reformers and the roman catholic church. The assembly of god ministers who were honest and open enough to search the scriptures to see if the oneness is true, and found it to be so, should not be castigated by those who are not open enough to search out these things. (after) Pentecost, the Christians continued to believe in one god, but they also believed that in Jesus they had seen god, that Jesus was god himself become flesh. They likewise were convinced that the power which they found at work within them was also god. Christians nurtured on the great central affirmation of Judaism, “hear, o Israel, the lord thy god, the lord is one,” were constrained to think of god as father, son, and holy spirit, three in one.
Solved> to the satisfaction of all who bear the Christian name, is that of the. . Most of them were also convinced that in some unique way, in Christ was both man and god and that the holy spirit was from god and is god.