As I pointed out in my original post most of the Germanic invaders of the Roman Empire in The Fifth Century were Arian Christian NOT Pagans. The Huns were Pagan, but the Goths were Arian. Years Ago I read the Franks of this time period were Catholic, but recently I have read the Franks were Pagan till they took over the last Roman Area of right is now France at which point their embraced Catholicism a opposed to the Goth's Arianism.
The fight between Arianism and Catholicism (And When I use the term Catholic I include what is now called the Orthodox church) was quite deep but the exact nature is obscure given the time period. We know what doctrine the dispute was over (Arianism said God Created Jesus and the Holy Spirit, Catholicism maintains God, Jesus and the Holy Spirit are one and the same, just different manifestation of God).
It seems Constantine lend to Arianism as he aged (He was baptized on his Death Bed by a Arian Bishop, through at least one writer thinks the Bishop was Catholic and only called a follower of Arian do to Constantius II preference for Arianism) and his sons seems also to be followers of Arianism. At the same time the overwhelming number of Bishops appear to be Anti-Arianism. The Various Council called by the aging Constantine and his sons seems to be attempts by them to have the Bishops accept Arianism. When Arianism was constantly rejected in these Councils Constantius seems to have arrested a few Catholic Bishops but very few.
Speculation indicates that the murders of Constantine's Relatives by his three Sons were to make sure only Followers of Arianism were in the family. Most of those who were killed appear to be Catholic not Arian.
As to the religion of the Roman Army, we have a similar confusion. Mirthism had been popular and subsidized by Diocletian and Constantine. When Julian Died in Battle the Army would pick a Catholic to lead them (which lead to the Catholics not the Arians being the Rulers of Rome in the last 1/2 of the Fourth Century). Just 20 Months previously the same Army had sided with Julian in his claim for the Throne. Julian was a follower of the old pagan religion (Though the Army may have backed Julian do to his recent victories over the Germans more than support for Julian's Religion).
I go into this for the Army decided who was to be Emperor in The Roman Empire. It appears the Army became more and more Catholic over the years, while the Auxiliaries (Mostly German Mercenaries in Roman Service) became Arians.
The best explanation for all of this is that Certain groups in Rome preferred Arianism's idea of God being superior over Jesus, thus Rome can be superior to the Germans. The Germans even seems to adopt this concept but drop it in the Sixth Century for the same reason the Catholics had rejected it, how can you be one church if you worship two different "gods" i.e. God and Jesus. As long as the Germans were willing to be tools of the Empire they accepted Arianism. Once the Germans rejected Rome as their master, instead treated the Empire as their Equal, the German Adopted Catholicism, thus making themselves Equals to the Romans.
Do not think the above thinking is wrong, Constantine and his sons probably had the last real Roman Army. Germans were in it, but they were NOT the Majority. Arianism would thus appear to Constantine and his Sons as a why to show the Germans they should accept second place to the Romans. The Chinese under the Ming Dynasty did a similar act with Buddaism and the Mongols, The Ming perfered Confusius to Budda for themselves, but wanted the Mongols to adopt Buddaism so the Mongols would become less warlike. Thus a dual track attitude might have been adopted, one for Romans (Catholicism) and anther to the Germans (Arianism).
When Jovian and than Valentian and Valens became Emperor after Julian, the Army was still overwhelming Roman, but this Army was destroyed by the Goths in the Battle of Adrianople in 378 AD. With that Destruction a new army had to be built up and that was the Army of Hired German Mercenaries that would lead to the Destruction of the Empire in the West.
Thus it appears Rome after Julian adopted a two track policy as to Christianity, one for Romans of Catholicism and the concept that EVERYONE was equal in the Eyes of the Lord, and another for the Germans of Arianism where hopefully the Germans would view themselves as Jesus was to God Under Arianism i.e Secondary but important.
This is the Best explanation I can come up with for Arianism and why it lasted as long as it did (and why it disappeared for all practical purposes within 50 years of the Germans occupying the Western Empire). The Disappearance of Arianism corresponds with various land reforms being implemented by the Germanic Invaders (Again viewing themselves and the Romans as one and the Same). Thus Arianism as shut out of the Empire, but encouraged among the Germans.
I go into this for often Religion difference do not reflect actual theology disputes but underlaying Economic and/or Political Disputes. For Example in the Sixth Century the Dispute in the Eastern Empire would be between the dual or single nature of Christ. Was Christ always divine even as he lived (The Single Nature of Christ) or did Christ have a dual nature, one divine the other Human (The Dual Natural of Christ concept). To today's modern ears this dispute sounds odd, who cares if Christ was divine while he was on earth? But this was the big dispute in the Sixth Century. If you looked at that Dispute the Single nature Concept came out of Egypt and the Dual nature out of Greece. As long as the Western Empire stayed part of the Empire this dispute was minor importance, but once the West had fallen the nature of Christ came to a head. Why? Simple The Single Nature Reflected what Egypt and the Dual Nature reflected Greece. With the West no longer part of the Empire these two sections were fighting for control over the Empire and themselves. Basically if you backed the Single nature of Christ you backed Egypt, if you backed the Dual nature you backed Greece. This dispute ended with the Arab conquest, for Egypt was taken out of the empire. The empire was reduced to its Greek Base. Gibbon in his Decline and Fall of the Roman Empire points out the fact you had various religious disputes from Constantine to the Arab Conquest but than nothing for 800 years. He could not answer why, for he could not see that the Religious disputes masked fights between the ruling elites of Egypt and Greece. Gibbon was a product of 18th Century England, another Country where Religion had masked Political fight. The Puritans had presented the Growing Middle Class, the Anglican Church the Old Nobility and the Catholics the Working Class. Thus the English Civil War was NOT over religion but who should rule England, the Middle Class or the Aristocracy? (With both fearing the working class thus both sides backed harsh anti-catholic laws). On the Continent the same thing was occurring but there the Catholics had kept the Aristocracy and working class within the Catholic Church. Thus the French Revolution had to break away from Religion for the new and growing Middle Class to triumph. Even here the Revolution took place only as the Working class represented Priests in the Third Estate voted to join with the Second Estate to form the National Assembly (An Act most French Bishops opposed but the Parish Priests voted for).
My point is Religion is often used as cover for some other dispute. At the Time of Constantine it appears to be a Fight Between the Roman Citizens (Catholics) and the Germans (Arians) in the Army. During the Time of Justinian about who should rule the Empire, the Greeks (Dual Nature of Christ) or the Egyptians (Single Nature of Christ). During the English Civil war between the Middle Class (The Puritans), the Aristocracy (The Anglican Church) and the Working Class (The Catholics in Britain). During the French Revolution the Revolution only succeeded when the Catholics Priests (not the hierarchy the Parish Priests) voted to support the Huguenot (French Puritans) dominated Middle Class over their fellow Catholics in the Aristocracy (Who had cease to practice Catholicism decades before).
I go into the above for most "Heresies" are minor and disappears quickly from History, the ones that stayed always had strong economic and/or Political power roots. The Catholic - Arian dispute lasted to long (and disappeared to quickly) to be anything but some sort of Political power dispute (Economic disputes tend to last a lot longer and than slowly disappear as the under laying economic dispute is either resolved, disappears or replaced by another economic dispute).
My problem has been trying to solve the underlying Political dispute. It has something to do with the Roman Army but what is hard to say today. I suspect up till the time of Constantine the Common Soldier followed the Mirthic Religion while in the Army, but before and after his Army Service he was a Christian (and was his wife and children, The Roman Ban on their Soldiers marring having been abolished during the Third Century). The Arians seems to have accepted this, while the Catholics rejected it. With the rise of Constantius II as Emperor (Constantine's Son) he wanted to make this normal. The problem was while the Army was Arian/Mirthic the Cities, bureaucracy and Christian Elite of the empire were Catholic. With the Destruction of the Army at Adrianople the Country split even further. The Army going more and more for German Mercenaries became more and more Arian, while the people of the Empire embraced Catholicism. The German stayed Arian for that is the first type of Christianity they were exposed to. Only as the German occupiers of the Western Empire started to see themselves and the Romans as one and the same did the Germans drop Arianism for Catholicism.
Books of the Early Church Fathers:
http://www.ccel.org/fathers2/On Arianism:
http://www.newadvent.org/cathen/01707c.htmInformation on Constantine:
http://www.roman-emperors.org/conniei.htmhttp://latter-rain.com/eccles/constant.htm