In his book The City of God, Augustine inadvertently exposed how Christianity led to Rome's downfall, even though the book was meant to counter these claims. Ignore Augustine's arguments and take the Romans' claims at face value. Christianity was a top-down takeover, starting when 90% of Rome's population was still pagan and crackdowns began against their native culture.
Today, we see similar de-racination attacks against Europeans in their own countries, driven by anti-white Marxism. If our society were to collapse and be conquered, and if future historians argued, 'Anti-white Marxism had no role in this! The USA was already crumbling economically, and invaders simply took advantage of this, making it just a case of one superior nation conquering another!' we would recognize this as clear nonsense. Yet, this kind of excuse is commonly accepted when discussing Rome's fall.
Trust the accounts of the Romans themselves, not the narrative from those who dismantled their cultural identity!