Why did the Romans embrace Christianity?
It was a way of enforcing cohesion in the Empire, which would have been difficult to control with all those different pagan/heathen religions. Enforcing a particular religion would have unified the Empire under the Emperor Constantine. There would still have been different pagan feast days, but they were left intact except that the reasons were changed. The midwinter festivals were changed to celebrate the birth of Christ. And the spring festival in honour of the fertility goddess Eostre was changed from celebrating the resurrection of the crops to the resurrection of Christ. In English-speaking countries it’s still called Easter, and fertility symbols like Easter Eggs and Easter Bunnies are still used. So the reason was control to maintain the Pax Romana, and without it Christianity would probably have remained a collection of minority cults or gone the way of other mythologies.
There were many, many reasons, most very practical. A great book on the subject is by sociologist Rodney Stark called The Rise of Christianity. He uses theories of economics and cost benefit analysis. I can’t remember everything but some items were very interesting. Women were given higher social status within Christianity (the Romans “aborted” baby girls by abandoning them on hillsides). Girls were brought up Christian and single women, often of wealth, helped create the circumstances where Christians simply reproduce more and at a faster rate than in the male centered Roman culture. They just outnumbered them in a few generations.
For the first 280 years of Christian history, Christianity was banned by the Roman empire, and Christians were terribly persecuted. This changed after the “conversion” of the Roman Emperor Constantine. Constantine “legalized” Christianity at the Edict of Milan in A.D. 313. Later, in A.D. 325, Constantine called together the Council of Nicea, in an attempt to unify Christianity. Constantine envisioned Christianity as a religion that could unite the Roman Empire, which at that time was beginning to fragment and divide. While this may have seemed to be a positive development for the Christian church, the results were anything but positive. Just as Constantine refused to fully embrace the Christian faith, but continued many of his pagan beliefs and practices, so the Christian church that Constantine promoted was a mixture of true Christianity and Roman paganism.
Two points: First, their were plenty of Christian sects, like the Coptics in Egypt and the early forms of what became the Gnostics who would have survived fine without Rome. It is only the Catholics and their get, like the Orthodox and Protestants, who we’d now be without. The Roman Church became a purely financial and political organization by the 8th century, and what we call Christianity now is a reflection of that. Second, none of the peoples you mention had any chance of destroying the “Idea of Rome”. They beat Roman armies, even sacked and occupied the City of Rome itself forcing the Seat of the Government to move to Constantinople, but the people still considered themselves Romans, and while they did the Roman Empire survived. If you study History none of them even wanted to destroy the Empire, they wanted either to be left alone, like the Celts, or to run it themselves, like the Goths and Vandals.
