Arianism developed around 320, in Alexandria Egypt 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.
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, 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. [Thus, Arianism teaches that Jesus Christ was a created being and was not God, but was to be worshipped, nonetheless.]
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.
“Arianism” is also often used to refer to other nontrinitarian theological systems of the 4th century, which regarded Jesus Christ—the Son of God, the Logos—as either a created being (as in Arianism proper and Anomoeanism), or as neither uncreated nor created in the sense other beings are created (as in Semi-Arianism).
[The modern-day Arians are none other than the Jehovah’s Witnesses.]
The Christology of Jehovah’s Witnesses is also generally regarded as Arian, given their views on development of the Trinity. In connection with this Jehovah’s Witnesses also believe the Holy Spirit is not an actual person but rather is God’s divine breath, God’s power in action.
“In modern times some Unitarians are virtually Arians in that they are unwilling either to reduce Christ to a mere human being or to attribute to him a divine nature identical with that of the Father.” (Encyclopædia Britannica)
Another group that may be considered Arian is the Church of God (7th day) – Salem Conference.
Aryan Nations is a white supremacist or “white Christian separatist” religious organization originally based in Hayden Lake, Idaho. Richard Girnt Butler founded the group in the 1970s, as an arm of the Christian Identity organization Church of Jesus Christ–Christian. The Federal Bureau of Investigation has called Aryan Nations a “terrorist threat”.
[Thus, it has nothing to do with Arianism.]