One of the important things to realize about schisms is that they can be very convenient things for peoples or rulers who have a need for a good excuse to distance themselves from a nearby power structure they don't want to be tied to. Thus you can find a pattern where people of a different social or ethnic background than the rulers at the seat of a religion's power will enthusiastically pick up a local heresy and promote it.
The situation in the 4th century was one where Rome was the overwhelming power in the Empire, and had a great deal of respect. The Greek cultural area was big and was in fact the source of the initially persecuted cult of Christ, but that battle had mostly already been won. The only other real cultural outlier of any power was Egypt. This was an old powerful, non Indo-European civilization that had been conquered by first Greeks, then Romans, and was essentially being plundered every year for its produce. If there's a place where you'd expect a desire for a cultural split, this was it. So it should be no surprise that in fact Arius and the two bishops who voted with him at Nicaea were from Egypt.
In the middle ages, the German invaders who conquered Italy and nearby territories hardly wanted to take orders from some guy in Rome. So they picked Arianism for this same purpose. At the same time the Eastern Romans (Greeks) used a set of squabbles that evolved into Eastern Orthodoxy.
So Arianism wasn't actually a very significant movement until the 5th century, which is when many German tribes overran the west, and took that schism up as a convenient way to make themselves independent of the Pope in Rome.
So by the 6th century, Catholicism was at a very low ebb. The pope was really only acknowledged in parts of Greece, most of modern-day France, and about half of the British Isles.
The east was under the control of the Eastern Roman emperor and his pet patriarch in Constantinople. Most of the rest of North Africa, all of Italy, and almost all of Illyria and Spain and Mediterranean France were controlled by Arians (iow: Germans). This included all the major cities of the West at the time (Carthage, Rome, Ravenna, and Milan). The rest of the British Isles and Europe were "officially" pagan.
Since the Franks were powerful enough and far enough away from the Popes, they never much bothered with Arianism. All the other German invader Arian rulers lost their territory to conquest (first to the Byzantines under Justinian, then mostly to the Arabs).
So basically you need to look at "heresies" as an ethnic culture war carried out by (mostly) non-military means.