Definitely the germanic footmen were the rats that swarmed the foundered ship of state, but I'd argue they managed it only once the horsey Goths and Huns had cracked the nut. Up until then the Romans cracked german heads as a regular sport for centuries, and only lost if they put pencil-necks in charge who led legions into swamps in winter....
Poitiers/Tours in 732 was pretty much the first stop on a charge that commenced at Mecca, so they were due for a halt. Not sure about Ummayid heavies, perhaps they were more of a Berber raiding party than formed Kwarazmian style katas?
From the Red Sea to the Loire valley is a fairly impressive run of wins for the horse vs the foot.
Very good point. The very real breakdown of civilization (in the West) meant there was not the urban administration to rally and arm concentrations of foot.
I liken the spread of the feudal horse culture to the mafia. Its all about honour, families, getting "made" (a knight), private wars (feuds), extortion (dues and levies) and pimped rides.
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