from wikipedia:
Arius taught that God the Father and the Son did not exist together eternally. Arians taught that the pre-incarnate Jesus was a divine being created by (and therefore inferior to) God the Father at some point, before which the Son did not exist.[4] In English-language works, it is sometimes said that Arians believe that Jesus is or was a "creature", in the sense of "created being". Arius and his followers appealed to Bible verses such as Jesus saying that the father is "greater than I" (John 14:28), and "The Lord created me at the beginning of his work" (Proverbs 8:22).[5] The latter quote has provided some controversy because it is technically speaking of wisdom. However, many people, notably Jehovah's Witnesses, believe that the wisdom in this proverb symbolizes Jesus Christ because he is later described in a similar way.[6]
Of all the various disagreements within the Christian Church, the Arian controversy has held the greatest force and power of theological and political conflict, with the possible exception of the Protestant Reformation. The conflict between Arianism and Trinitarian beliefs was the first major doctrinal confrontation in the Church after the legalization of Christianity by the Roman Emperors Constantine I and Licinius.[7]
The controversy over Arianism began to rise in the late 3rd century and extended over the greater part of the 4th century and involved most church members, simple believers, priests and monks as well as bishops, emperors and members of Rome's imperial family. Yet, such a deep controversy within the Church could not have materialized in the 3rd and 4th centuries without some significant historical influences providing the basis for the Arian doctrines. While some historians define and minimize the Arian conflict as the exclusive construct of Arius and a handful of rogue bishops engaging in heresy, other historians recognize Arius as providing a conservative response against the politicization of Christianity, or a defender of original Christianity. Of the roughly three hundred bishops in attendance at the Council of Nicea, only two bishops did not sign the Nicene Creed.[8] However, to minimize the extent of Arianism ignores the fact that extremely prominent Emperors such as Constantius II and Valens were Arians, as well as prominent Gothic, Vandal and Lombard warlords both before and after the fall of the Western Roman Empire.
After the dispute over Arius politicized and a general solution to the debate was sought – with a great majority holding to the Trinitarian position – the Arian position was officially declared to be heterodox. Lucian of Antioch had contended for a christology very similar to what would later be known as Arianism and is thought to have contributed much to its development. Arius was a student of Lucian's private academy in Antioch.
While Arianism continued to dominate for several decades even within the family of the Emperor, the Imperial nobility, and higher-ranking clergy, in the end it was Trinitarianism which prevailed in the Roman Empire at the end of the 4th century. Arianism, which had been taught by the Arian missionary Ulfilas to the Germanic tribes, was dominant for some centuries among several Germanic tribes in western Europe, especially Goths and Lombards (and significantly for the late Empire, the Vandals), but ceased to be the mainstream belief by the 8th century, as it was successfully crushed through a series of military and political conquests, culminating in the political-religious domination of Europe over the next 1,000 years by Trinitarian forces in the Catholic Church. Trinitarianism remained the dominant doctrine in all major branches of the Eastern and Western Church and later within Protestantism until modern times.