In 410, when the Romans saw the Visigoths streaming over the Seventh Hill to sack Rome, I doubt any of them comprehended that would be the abject end to their empire and Roman culture itself.
Of course Rome was rotting from the inside-out for almost a century beforehand. The growing immigration numbers of barbarians, Goths and other conquered peoples who were immediately made Roman citizens for the purpose of expanding the Empire’s welfare rolls and tax base, had been attacking and eating away at Rome’s wealth, sovereignty and security for many decades. Rome had already lost her unique culture as it had absorbed so many cultures that refused to meld with the Roman culture – that there was little to distinguish what was once Rome. By 410 – immigrant barbarians had outbred Roman people themselves, and stood ready for Alaric to take revenge and burn the capital – and the entire Roman culture to ashes for the history books.
Today, like Rome – Western Christian culture is being outbred and soon the barbarians are going to outnumber the native peoples. Only there will be no need for an invasion – they are already rising among us.