Thanks. This is more what I am looking for. I am not looking for arguments, but over the years I have kind of picked up a hobby of trying to figure what all these first millenial sects believed, and what separated them from other Christians at that time.
Do you know of any good books or web pages on these sects?
well, there is a very good book in German called "the Ancient Churches of the East" -- i've read the translation in French and know there is one translation into Polish, but I don't believe there is any translation into English
I presume you mean first millenium Christian groups, right?
I would prefer to use the term groups to remove any connotation with sect
But, from Apostolic times we see a distinct group of, let's call it "orthodoxy" ( the bulk who hold to the gospels and some letters of Paul (not all were initially acknowledged by all -- Hebrews being a case in point) and the first 2 letters of Peter and of James (the book of revelation was rejected by most for a long time until canon was closed)) and those who "orthodoxy" identify as outside based on dogmatic beliefs -- Mandaeans (who hold even today that Jesus was a false messiah and john the Baptist was the real one), Gnostics, etc
But, they retained the same belief -- not quite hard to believe when you think of the quality of Roman roads and communication -- the emperor could get a message from Arabia-Petra to Scotland in a few days and the common man a little longer. Travel by Roman road was sure and quite fast (in fact not achieved again in Europe until the late 1800s)
Anyway -- the first big split we can read of is the Assyrian Church -- based in the Persian Empire
I'll stick to that one in this post -- you of course know that there was a rivalry between Rome and Iran right from the time of Crassus in 50 AD?
After Alexander the Great died, his empire was split between his generals -- the Diodache. One got the Greek/Macedonian heartland, another strong one, Ptolemy got Egypt and the strongest, Seleucus got what is now Syria, Turkey, Armenia, Iran, Iraq, Turkmenistan, Afghanistan and Baluchistan
But the Seleucid empire shriveled from the time Seleucus died -- but not before Antiochus IV Epiphanius despoiled the Jewish Temple (a good read is the book of Maccabees -- book 1 for the historical basis), shrivelling down by 100 AD to just about a small portion of what is now north-eastern Syria
At the same time a loose confederation of Iranic peoples, the Parthi rose in what is now Uzbekistan and took over much of Greater Iran. For a long time, there was no issue with Rome as Rome was (from 300 BC to 50BC) involved in the Western Mediterranen. But, by 100 BC, it had taken Epirus (albania) and nudged into Greece. Then Pompey the Great in 60 BC took over Jerusalem and much of the eastern Mediterranean bar Egypt. The 3rd member of the Pompey-Caesar-Crassus triumvirate, Crassus, looked for glory against the Parthians but ended up with a massive defeat (one of the most massive for Rome ever) at Carrhae -- present day Harran in Turkey on the borders with Syria where 35,000 legionaries were lost. That started the Roman-Parthian wars. These continued on and off until Trajan -- now remember that the Parthians were a confederation, so Rome had an easy time. Trajan destroyed them and pushed the Roman empire to the Persian gulf, to what is now Kuwait
But, in doing so, they destroyed the Parthians and set the stage for a far more centralized and stronger power -- the Sassanids to arise
The House of Sasan was Persian, of the lineage of Khorush the Great (Cyrus the Great) and looked on their mission as a divine mission granted by Ahura Mazda to reconquer the Persian lands (note: Darius the Mede, the successor to Cyrus, literally ruled over 40% of the world's population) and to fight on the side of the god of light (Ahura Mazda) against the darkness (Aingra Mainyu)
Rome versus Persia was a centuries long war - from 250 AD, through to the defeats of Valerian (when, for the first time, in 256 AD, an Emperor was captured in battle) right to the final treaty, signed just before Islam came charging out of the desert in 600 AD
Rome and Persia hated each other -- the Romans believed they had a manifest destiny to spread their dignitas, their humanitas, their civilisation. And the Persians believed that they had a divine mission to spread their own empire
Christians in Persia and Iraq were on the fault line
initially, under the persecutions of Dacian, Valerian, the Macriani, when Christianity was outlawed, the Shahenshah of Persian welcomed the Christians (the enemy of my enemy) and there are rumors that Shapur II even converted to Christianity (rumors only, 0 proof)
BUT, the Christians overplayed their hand and burnt down zoroastrian fire-temples, prompting a push back against them
This was momentary, but what really turned the tide against Christians was a century later in 395 AD when Theodosius II made it a state religion -- now, if your mortal enemy makes a religion state religion, you immediately view the adherents of that religion in your country as your enemy (which is the reason for much of the medieval Catholic-Protestant-Orthodox bloodshed)
The only way for the Christians in Persia to survive was to say "hey -- those are not our type of Christians, we split"
then, you should ideally visit Kerala or read about the Syro-Malabar, Syro-Malankara, Syrian Orthodox and Jacobite Churchs there -- it will give you an insight
And in Syria itself you have the Syrian Melkite Church which is intriguing