A people who had mastered superior ship-building and sailing technology would be a threat to all coastal civilizations, much like the Vikings and Muslim corsairs of North Africa strongly contributed to the Dark Ages about two thousand years later.
A large force, arriving from the sea without warning, can loot and pillage an area, and disappear over the horizon before any response can be mounted.
Make ocean trade unsafe, and things collapse.
***A large force, arriving from the sea without warning, can loot and pillage an area, and disappear over the horizon before any response can be mounted.***
So the good citizens of Baltimore Ireland found out in the reign of Charles II.
“the Vikings”
They were off for Spring Break from The Great White North and ran out of ca$h and had no idea that there were no ATMs in England.
They were forced to make do with Monasteries.