Arianism developed around 320 in Alexandria Egypt and concerning the person of Christ and is named after Arius of Alexandar. For his doctrinal teaching he was exiled to Illyria in 325 after the first ecumenical council at Nicaea condemned his teaching as heresy. It was the greatest of heresies within the early church that developed a significant following. Some say, it almost took over the church.
Arius taught that only God the Father was eternal and too pure and infinite to appear on the earth. Therefore, God produced Christ the Son out of nothing as the first and greatest creation. The Son is then the one who created the universe. Because the Son relationship of the Son to the Father is not one of nature, it is, therefore, adoptive. God adopted Christ as the Son. Though Christ was a creation and because of his great position and authority, he was to be worshipped and even looked upon as God. Some Arians even held that the Holy Spirit was the first and greatest creation of the Son.
At Jesus' incarnation, the Arians asserted that the divine quality of the Son, the Logos, took the place of the human and spiritual aspect of Jesus thereby denying the full and complete incarnation of God the Son, second person of the Trinity.
In asserting that Christ the Son, as a created thing, was to be worshipped, the Arians were advocating idolatry.