@Flash
It wasn't quick though was it? Certainly not quick enough to fit into the pattern you are asserting. They may have lost Alexandria in 671, and perhaps you can claim that as important, but they lost the battle of Manzikert in 1071. That is where they went into their fatal decline and is way way way outside of your cycle. And in both cases they lost chunks of empire to equivalent empires without any dark age ever descending anywhere so this loss of civilisation you are whittering about doesn't occur irrespective.
The Byzantine Empire reached its peak in 555, about a century after Rome's fall and about half a century after my supposed global dark age begins.
However, even at its peak, it was a little over half the size of Rome, and a century after that, about a fifth of Rome.
It paled in comparison to Rome even at its height, really it was Rome, it was Rome on its way out.
I have modified my cycle.
It's now a 2000 year cycle instead of a 1500 year cycle.
The winter solstice, which signaled both the death of the 2nd global civilization (which saw the rise/fall of Rome, Greece, Persia, India and China) and the birth of the 3rd universal civilization (which'll see the rise/fall of Europe and its offshoots), which's is ours, was in 1000 AD, its spring equinox was in 1500, its summer solstice was in 2000, its fall equinox will be in 2500, and its winter solstice, its death/the birth of whatever's to come, will be in 3000 AD.
That's a lot of speculative stuff you are presenting there. Capitalism is really a very sustainable system and none of those resources are actually running out. WW3 to be fought over something like that is really a massive excercise in wishful thinking.
Capitalism is the antithesis of sustainbility, its faulty premise is endless growth.
There's only so much oil, uranium and so on in the world.
It's not that these resources will run out overnight, it's that demand is outpacing supply at an accelerating rate, which'll send prices skyrocketing.
It's getting increasingly difficult to find and extract these resources, increasingly inefficient.
Additionally there's climate change to worry about.
No combination of green technologies, each one with problems of its own, will makeup for coal, gas, oil, uranium and so on, all of them incredibly powerful and hitherto relatively easy to find and extract, furthermore it will cost trillions upon trillions of dollars to replace them with green techs and decades.
We're going to have to dramatically power down our civilization, or perish, there's no alternative.
A third instance wouldn't give you statistical significance. Your cycle has to run for tens of thousands of years before it becomes a basis for statistical prediction. Sorry, maths won't help you here, maybe the 97th generation of your man seed will inherit mathematically sound knowledge from this discussion, but you won't live to see it.
There is no exact point at which something becomes statistically significant, two instances of a thing is significant, two more instances is more significant, it's a continuum, a spectrum.
If A then D then...?
Of course it could be anything, it's not a lot to go on, but having nothing more to go on, I"m going to go with G.
Your spring summer autumn and winter theme for civilisation is the sort of thing I expect to read in a Victorian era text book, the empty nonsense that used to be popular because it provided a handy pseudo-explanation for the rise of the various empires that posed as indirect successors to Rome. It's unsophisticated junk food for the soul. If you factor in effeminacy as part of the final decline of a decadent civilisation you are basically Macaulay risen again.
Civilizations are organic processes, super organisms.
They have a life span.
Virtually every civilization born at some point died.
They have a beginning (winter), they can't materialize fully developed out of the aether, then a rise (spring), then they peak, stagnate (summer), then they fall, and then they die (winter).
Granted there are exceptions to this rule, some civilizations might rise, then stagnate, then rise some more, or some might be swiftly destroyed while they're still in the process of rising, but typically civilizations do most of their rising in one period, their stagnating in the following period, their setting in the subsequent period before perishing.
Rome is the quintessential example but many followed this path.
And now I'm just applying this same principle, a principle noted by many historians throughout the ages, to civilization itself.
The west is still growing, but it's growth has slowed down, economically, even technologically, not much other than communications has developed in the last few decades, nothing like how fast it was growing, or how fast China and India, which're attempting to ape our 'success', are growing now.
We're in late summer now, and in another century or two we'll enter the autumn phase.
There can also be like a marriage of civilizations, like how European civilization had both Greco/Roman and Judeo/Christian origins.
Civilizations will always rise/fall, everything that's born dies, this seems to be the way of things.
The problem with civilization is I don't think we've figured out how to do this gracefully.
We get too enamored with ourselves and the things we build.
We rise too quickly, bite off more than we can chew sort of speak, and fall just as quickly.
excessive materialism, hedonism and even science, technology leads to a tumultuous death from which it'll be difficult if not impossible for subsequent peoples to spring back from.
I wouldn't say civilizations fall because of effeminacy.
However, men and women are neurologically different, we have different strengths and weaknesses, which've been shaped by our physiology, and which'n turn, have shaped our physiology.
Sexually we're getting further and further away from nature, we can see this in both the feminization and asexualization of men, as well as the masculinization and asexualization of women.
As civilization advances beyond reason, sexual specialization becomes less and less relevant, and as sexual specialization becomes less and less relevant, civilization advances beyond reason, and so the two are codependent phenomena.
But even if we permit the analogy for a laugh, you've really got no likely grounds to make your claim that we are the fatal winter of our civilisation unless you resort to the doomsday daydream you already tried. If you wanna go that way, then fine, we can cover why water and food are obviously not "(non)renewable resource" and why those others you mentioned are available in qunatities sufficent to last us well past the boundaries of your fictional cycle.
There's a reason why the non in nonrenewable resources was in brackets, I'll let you figure out why.
Sure, let's go down that road.