When I was a lurker, I saw this link.
Along with a question I had about barbarians, its what inspired me to sign up in this UNRV forum.
So I have to ask why? Why did the Romans fail even with use of their mighty armies as the OP pointed out while Church missionaries and priests eventually converted entire regions and barbarian peoples Rome could never subjugate like the Picts of Scotland even with military force (often suffering immense defeats when they entered regions like Northern Netherlands)? Yet the Catholic Church was not only able to convert these various regions and barbaric tribes through peaceful means yet also make even the most backwards and warlike of them like the Germanics of Northern Germany submissive to the Church and adopt order and civilization! How did the Church do it despite advocating a religion that condemned violence esp war and advocated order and stable civilization where as mighty armies of the most powerful civilization to have ever existed in Europe have failed so miserably?
It just doesn't make sense that the Germanics north of the Rhine who did human sacrifices and killed and killed each other for fun would eventually find a religion where a God sacrifices himself for mankind appealing to convert to! The Picts committed preying of the weak because much of their culture vouched the rule of the strong and violence as the prime laws-yet all of Scotland would convert through peaceful missionaries to Christianity which is a religion that ruled for the rich and strong to aid the poor in poverty.
The Irish clans practised nature worshipping but some how Catholic priests convinced them that it is better to live in villages and have a strong organized government than to live as random settlements in the woods and other uncultivated wilderness.
Its simple to miraculous that the Catholic Church didn't have to send knights to convert Northern Germany but did this with a couple of martyred saints! And that the Picts could be convinced by hermits wandering around to start sending charity to the poor and convert to a religion advocating responsibility to watch over the weak and needy! And for people who lived in the wild for centuries in Ireland to throw away their old Gods and follow a Church that encourages a more urban livelihood!
All without needing to send massive armies! The Romans tried to civilize these warlike savages through conquest and subjugation but they failed (often facing mass slaughter of their military forces sent to these barbarian areas they can never actually colonize). But the Church did it through peaceful means with just a couple of preachers voluntarily going across Europe!
How did this unbelievable miracle happen?