"The purpose of the council was to resolve disagreements in the Church of Alexandria over the nature of Jesus in relationship to the Father; in particular, whether Jesus was of the same substance as God the Father or merely of similar substance. St. Alexander of Alexandria and Athanasius took the first position; the popular presbyter Arius, from whom the term Arian controversy comes, took the second. The council decided against the Arians overwhelmingly (of the estimated 250-318 attendees, all but 2 voted against Arius)."
-Wikipedia--Council of Nicaea
The council was in 325 A.D.
"St. Alexander of Alexandria, Pope of Alexandria, date of birth uncertain; died April 17, 326.
He is prominent because his appointment to the patriarchal see excluded Arius. Arius had begun to teach Arianism in 300 when Peter, by whom he was excommunicated, was Patriarch. He was reinstated by Achillas, the successor of Peter and then began to scheme to be made Patriarch. When Achillas died Alexander was elected, and Arius was irked because he had been passed over. Alexander tolerated him in the beginning, but came to dislike Arius. Finally Arius' teachings were condemned in a council he called in Alexandria in 318, and later on in the Council of Nicaea in 325, which Alexander attended and whose Acts Alexander is credited with having drawn up."
-Wikipedia--St. Alexander of Alexandria
Arianism was not ever considered as biblically sound.
If you're wondering about the books that were excluded from the canon, all of them were written a long time after the apostles died.