The Great Stirrup Controversy
en.wikipedia.org
en.wikipedia.org
or one can say that warming climate (which resulted in Roman Empire fall and led to the rise of the Franko/German territories to the north of it) allowed for heavy cavalry which would otherwise wouldn't get through the swampy forests which were there before. If you look at dry regions at other places/times you'd see pretty heavy cavalry there too.
https://en.wikipedia.org/wiki/Cataphract
"While they varied in design and appearance, cataphracts were universally the heavy assault force of most nations that deployed them, acting as "shock troops" to deliver the bulk of an offensive manoeuvre, ... While their roles in military history often seem to overlap with lancers or generic heavy cavalry, they should not be considered analogous to these forms of cavalry, and instead represent the separate evolution of a very distinct class of heavy cavalry in the Near East that had certain connotations of prestige, nobility, and esprit de corps attached to them. In many armies, this reflected upon social stratification or a caste system, as only the wealthiest men of noble birth could afford the panoply of the cataphract, not to mention the costs of supporting several war horses and ample amounts of weaponry and armor."
But it was 500+ years between the fall of the Roman empire and heavy cavalry owning the battle field in Western Europe?
On the other hand, you can partly derive the political system from technological changes too (I.e. without the socialist scare you don't get fascist regimes, and without the industrial revolution you don't get socialism)
As for me, I'd like to think that a bit more nuanced approach is better. Yes, stirrups might enable men to use horses in new ways and to brace themselves on horseback. But this sort of expensive heavily armoured cavalry cannot exists in a vacuum. It needs a class of wealthy people who can buy armour and horses. The wealthy need some sort of motivation to train themselves as warriors and so on. If you are interested in the subject, The Making of Europe: Conquest, Colonization and Cultural Change, 950-1350 by Robert Bartlett [1] is an excellent book on the subject.
[0] https://en.wikipedia.org/wiki/Technological_determinism
[1] https://www.amazon.com/Making-Europe-Conquest-Colonization-C...
A chicken/egg cycle, initialized by temporary imbalances that created a stable system: an increased advantage of cavalry over infantry drives up the price for "protection", which in turn feeds the horses. With less advantage of cavalry over infantry, the class system would have been much less pronounced.
In the spirit of "strange women lying in ponds distributing swords": a fluent socio-economic power structure was converted into an intransparent class system self-stabilized by the barrier of entry imposed by the inherent cost of heavy cavalry.
I agree. I think that a given technology has requirements and consequences that determine a lot about the society it is in, but it also presents various possibilities that will be determined by external factors, such as politics.
[1] I hesitate to call it 'literature'...