How accurate does RationalWiki describe the history of early Christianity? I am asking from a secular historical perspective, not a Christian perspective.

"The beginning — Jesus of Nazareth and Saul of Tarsus

In the beginning was probably a man named Jesus of Nazareth (who would have been called Yeshua in his day), a wandering preacher in Galilee. (Even though the evidence for his existence is scant at best, most Christians will treat claims that he didn't exist as trolling.) He was probably born in Nazareth (the story about Bethlehem was almost certainly a fabrication invented to fulfill a prophecy), and was born at some time around the year 1 CE (conflicting, mutually exclusive accounts make it impossible to determine when exactly).

He lived as a rabble-rousing apocalyptic preacher until the Roman colonial authorities executed him for the crime of sedition longside two other rabble-rousers (probably bandit chieftains rather than thieves). The accounts of the trial under Pontius Pilate and before the Sanhedrin are almost certainly fabrications — they do not match what is known about the people concerned or how the Sanhedrin worked. His death was unremarkable and indeed unremarked on by anyone writing at the time*. The first person to actually write about Jesus, Paul of Tarsus (St. Paul), admitted to never having met him. Paul's version of Christianity is sufficiently different from that which has been ascribed to Jesus (as outlined in the Gospels, themselves unreliable sources as to what Jesus actually preached) that there are regular rebuttals of the idea that St. Paul founded Christianity. Indeed the central thesis of Reza Aslan's Zealot is that the Jesus that Paul preached about was more or less a fabrication. What is certainly true is that Paul did his best to convert non-Jews to follow Jesus — a program out of step with most rival sects of Early Christianity, which concerned themselves solely with winning converts among the Jews. Paul's ideas generally won out, and over the next few hundred years Christianity spread out. However, even in his own time Paul noted that there were people "corrupted from the simplicity that is in Christ" by "another Jesus, whom we have not preached," "another spirit, which ye have not received, or another gospel, which ye have not accepted", which suggests that there were already multiple forms of proto-Christianity among the Gentiles that were spreading independently of one another. By c. 180 CE this fragmentation had become so bad that Irenaeus wrote Against Heresies, a 5-book, 168-chapter work detailing the many deviations from the "true" faith.

Constantine the Great and the First Council of Nicaea (325 CE); the establishment of Orthodoxy

Constantine the Great (272-337) was very ambitious — he had to be to become Roman Emperor (306-337). And, possibly because of his mother, Saint Helena of Constantinople, and possibly because of opportunism, he was sympathetic to Christianity. And he also liked power. So he gave the various churches a chance to sell out: support him, and raise him to the status of equal-to-apostles, and he'd stop the persecution of them, and indeed offer to prefer them within his Empire. Which they did (the whole thing wasn't quite as nakedly mercenary as that, of course).

There was one other condition — the Christian Churches had to sort out what they actually believed, which they did at the Council of Nicaea (325) — in the process nailing down establishing a lot about the doctrine of the Trinity, and throwing Arius and the idea that the Son wasn't equal to the Father out of the Church — and exiling him. (On a ghoulish side note, Arius died (336) by shitting out his bowels the day before he was due to be reconciled with the Church. Cholera, divine judgement, or propaganda? You decide!)

The Orthodox Churches' (including the Roman Catholic Church) claim on The Truth is based on how old they are — or, as they call it, Holy Tradition. (This would make the Armenian, Coptic, and Ethiopian Churches pretty important in history and tradition — unless one's idea of west-Asian desert monotheist Christianity reflects a degree of Eurocentrism.) In the Roman Catholic Church, Magisterial infallibility on matters of morals and ethics is actually a whole lot more important than the much more famous 19th-century doctrine of Papal infallibility, which the Vatican has only ever invoked a handful of times.

The Council of Nicea established the Nicene Creed, which lays down the Trinity, Salvation, Judgement, and Heaven — and a majority of individual Churches have accepted this as a baseline ever since. An update at the Council of Constantinople in 381 CE also added the Virgin Birth and the resurrection of the dead — both commonly understood as a basis for European Christianity. The books of the Bible were settled in the West by 405 CE, but not all the Orthodox churches agree - let alone various Churches of the East. There was, however, a lot of discussion about which texts to include."