Pulling this to the red-headed stepchild of the general threads because it is VERY off-topic.
The "civilized urbanite vs uncivilized redneck" concept is 100% universal, as far as I am aware, and has been one of the most consistent sources of conflict in the modern era. I'm not as familiar with the pre-modern period, but from what I know of ancient history (Rome, Greece. Egypt, etc.) the idea may well be baked into our DNA. The rednecks almost always lose out compared to urban populations, too. For example:
The French Revolution's War in the Vendée, and the Reign of Terror it sparked? Killed shit-tons of random rural people in the name of Jacobin (so, Parisian urbanite) ideals. My personal favorite being the hyper-insanity that was the so-called "Temple of Reason" and the subsequent
Cult of the Supreme Being. All of which served as convenient distractions from the fact that urban Parisians had looted rural areas and Catholic churches to pay for their newly enlightened lifestyles. Paris itself lost 1500ish people to the Terror's purges: meanwhile the Vendée lost
at least a fifth of the region's population.
Same with the Russian Revolution. The Bolsheviks (who were almost entirely based in urban areas) took over the workings of the country, and started killing
relatively wealthy peasants called
Kulaks and confiscating their grain and property to fuel their own development. There was a whole system of rhetoric blaming the peasantry for capitalistic resource hoarding despite the fact that most Kulaks had very little money.
There are hundreds-if not thousands-of historical examples of bigotry against rural populations, and "redneck/hillbilly" is just the latest one in the anglosphere. I'm not sure if its because the population undercurrents you mentioned lead to cultural differences, or if its specifically something to do with the urban/rural divide, but you are very much onto something. It's a concept not openly discussed in a lot of academic circles (at least not in the US ones) either, because it has some very uncomfortable implications to it for the highly educated bigots out there.
It definitely dates to at the very least classical Greece, which had plays mocking the illiterate rural population, and where the Aetolian League (which had no major poleis and was derided for consisting entirely of rural hicks).
Although the Aetolian League kept winning until it finally got smacked down by the Romans (their erstwhile allies. Just... never trust a Roman).
Republican era Romans had a very high and idealised opinion of rural life, but well, that was the
idealisation. In practice, they sucked resources out of the countryside to support the cities, and rural citizens seldomly got the opportunity to participate in the political process on account of Rome's political system effectively limiting it to residents of Rome. Not
legally, and there were opportunities to get around the logistical difficulties for some, but in practice.
The term
pagan originated as a term for, well, hillbilly. And because all those hillbillies couldn't understand the glory and truth of that newfangled Jewish God that the citydwellers were starting to worship, the meaning of pagan eventually transformed into what we use it as today.
This being said, specifically in the American context, it's a pretty new phenomenon. Thomas Jefferson practically idolised rural life, Lincoln and Theodore Roosevelt benefitted immensely from their rural backgrounds/roleplaying as having one for a while.
American media still focussed heavily on rural life as archetypical and ideal throughout the 1950s and 1960s. It was in the late 1960s to early 1970s that this shifted decisively in favor of the city, simply as a consequence of the relatively growing percentage of the urban population (and its greater per capita income), making it a more attractive market to cater to.
I'm not sure I'd agree with that part. See the barbarian invasions of Rome, the Mongol conquests, the Almohads, etc.
There's quite a lot of examples of an uncivilized rural people conquering a decadent urbanite civilization.
Bit of a difference between states duking it out and resource conflicts within a state.
That aside, "Barbarian" successes were the exception,
not the norm. And without exception, they succeeded due to their targets undergoing a severe crisis
beforehand. When it was unified and not fighting itself, China routinely smashed the tribes to the north. It was only when China was divided or engaged in one of its hilarious civil wars that the tribes ever had a chance.
And in Rome's case, the problems started with the crisis of the 3rd century, which sharply reduced wealth generation, while the Germanic tribes along the Rhine and Danube got the opportunity to coalesce into proto states and the Sassanids formed into a credible threat exceeding the preceding Parthians.
The 4th century saw the rise of Christianity, the establishment of monastic orders, a return to piety. It also saw ever growing
deurbanisation, with the rich citizenry fleeing the cities in favor of rural estates, and monetary interests interfering with the state's ability to collect taxes or to conscript soldiers.
Rome at its most urbanised and decadent was the Rome of the 1st century BC to the 1st century AD. This was the Rome of Lucullus and Crassus, of Caligula and Nero.
This Rome
never stopped growing.
The Rome that fell was a Rome of bishops and monks, of rural estate holders desinterested in supporting the state over their own wealth, disincentivised from releasing their labor force for the army.
It was the least decadent, least urbanised Rome had been in six centuries.
And the richer, more urban, more decadent half of the empire?
That was the one to survive for another thousand years.