The spread of Christianity and the spread of non-Italians in the Roman Empire posed big challenge for the future existence of it. The reason for this was that both of these trends had one very powerful common thing, destroying the core of the Roman Empire, in political, ethic, and religious manner. The Christianity was quickly coming on top of the ancient Roman religion, which was the basis of the society, and once it was pushed on the margins and eventually in the past, it created much different social structure in Rome. The ethnic composition of the empire was too rapidly changing, with more and more non-Italians being part of it, and they started to greatly outnumber the Italians. That resulted in lesser loyalty to the empire, as the non-Italians didn't really saw the Roman rulers as the Italians did, but they were seeing as invaders and suppressors. Eventually this resulted in weakening the empire from the inside, which was one of the prime reasons why it crumbled.
