Excerpts from Books and Wikipedia
"The Christian church had universally acknowledged, since its beginnings, that Jesus partook in both human and divine natures: 'Jesus is Lord,' as J. N. D. Kelly remarks, was the earliest and most basic confession of Christianity. Christ, according to the earliest Christian theologians, was 'indivisibly one' and also 'fully divine and fully human.' . . . a Christian priest named Arius had begun to teach yet another doctrine: that since God was One, “alone without beginning, alone true, alone possessing immortality, alone wise, alone good, alone sovereign,” the Son of God must be a created being. He was different from other created beings, perhaps, but he did not share the essence of God. Arius, who served in the Egyptian city of Alexandria, had been gathering followers and vexing his bishop,* who had finally excommunicated him. . . . But neither the bishop nor Arius was willing to yield, and in desperation Constantine called together a council of church leaders to settle the question. . . . In 325, at Nicaea, the Christian church and the government of the west clasped hands. One might wonder why Constantine, who didn’t have any trouble reconciling his belief in Apollo with his professed Christianity, cared about the exact definition of Christ’s Godness. In all likelihood, his interest in this case wasn’t theological but practical: to keep the church from splitting apart. A major breach would threaten Constantine’s vision of Christianity as a possible model for holding together a disparate group of people in loyalty to an overarching structure. [Bauer: Ancient World, p. 8-10]