In my view, what favored Constantine in the Early Middle Ages was the strengthening of the Eastern Roman Empire (whose capital is currently called Istanbul, but to me, it's Constantinople), at the expense of the rotting borders of the Western Empire. This led to the looting of Rome and the establishment of the Ostrogothic Kingdom under Theodoric.
From a religious perspective, and regarding the schism that occurred (many centuries later), it was undoubtedly a revolution.
It's fascinating how state and church became deeply entwined around that time. My opinion is probably worth less than your zero times zero, not least because I have awful retention of what I've read. As far as I can see it, Constantine was looking for a religion that he could use to bind the people of the Empire together heart and soul as well as body. The West was lost eventually because the Empire no longer had resources to sustain and defend it, while at the same time the 'barbarians' were actually becoming more civilised and more capable. It's fascinating how all this impacted on the way the Church developed. In the East it was under the tight control of the emperors until the fall of Constantinople. In the West there was chaos interspersed with volatile kingdoms set up by the invaders. But the one constant in the West was the Christian Church - OK a lot of the invaders brought Arianism with them, but they weren't stable over the centuries. The Western Church in Rome was lucky that it had some very great and pretty crafty patriarchs in Leo the Great before the fall of Rome and Gregory the Great afterwards. The See of Rome found itself at the heart of political as well as spiritual cohesion and continuity, and started building a sort of Church hegemony across the West. It was passive power to a great extent, but the temporal rulers found it expedient to give the Bishop of Rome a kind of ascendency and power that didn't exist for the Eastern patriarchs. I think this more than anything else pushed the Western and Eastern churches apart until the great schism finalised it - the West needed the Pope to have ecclesiastical supremacy because the essential temporal power that went with it was what held societies all across Europe together. The Pope wasn't anything like an emperor of course, but more like a sort of godfather of all the various monarchs concerned.
With the Council of Nicaea, which took place a few years after the capitulation of the Praetorian Guard:
The Council issued several fundamental decisions:
1_-> Condemnation of Arianism and affirmation of the full divinity of Christ.
2_-> Drafting of the Nicene Creed, the first official declaration of Christian faith, still recited in Sunday liturgy today.
3_-> Setting the date of Easter, establishing that it be celebrated on the first Sunday after the full moon following the spring equinox, regardless of the Jewish Passover.
4_-> Rules on the conduct of clergy and principles of ecclesiastical discipline.
In my opinion, John, Constantine was simply an INFJ who saw centuries of history materialize before his eyes, like a seer.
A good question to ask is how, after the Great Schism of 1054, the Catholic and Orthodox Churches maintained shared ethical-religious boundaries, despite being so different
Could Constantine have had some kind of intuition about all this? I think you're right - whatever he had, it worked as well as anything probably could and better than most of the alternatives. I guess his immediate successors had an up and down relationship with Christianity, from what I remember, but maybe because of his actions it fed the following history of the world for 1500 years, better than perhaps any other strategy would have done.
I'm not surprised the East would eventually have nothing to do with all this in the West and a split was inevitable as long as the Pope claimed authority over all of Christendom. As far as I can see, the Bishop of Rome was traditionally always first in honour among the patriarchs, but not in authority. It's weird how the circumstances of the two suddenly switched after the fall of Constantinople - since then the Orthodox in many places became politically a subordinate religion to Islam and that has strongly coloured their culture and their relationship with Rome - a reversal of the situation immediately after the fall of Rome. Of course there was also a divergence in ecclesiastical language too, and after a few hundred years of Dark Ages, hardly anyone in the West would understand Greek until the Renaissance.
It's really sad because I can't see any severe doctrinal differences between Orthodox and Catholic - it seems to be more a matter of emphasis. I suspect there is greater difference between the various Orthodox traditions than there is between the main groups and the Catholics. It's a pity that our lot had to mess about with the wording of the Creed without a proper Ecumenical Council to deal with it, which is a legitimate bone of contention on purely religious grounds, I guess.