So how did the first democracy die? If it wasn't sexual degeneracy, what was it?
OK, there's more to it than that, including rampant flattery, demagoguery, impiety, and hubris, but it all starts and ends with the same thing that created and then destroyed the mighty 16th century Spanish empire, free money. In the case of the Spanish, it was their exclusive monopoly on looted Mayan, Aztec, and Inca silver (and gold, but especially silver). While Spain was using that money to build the world's mightiest army and navy, they were also using that money to buy food and manufactured goods from every other nation on Earth. And when the silver ran out, all they had left was their military. And when they lost their military to a British navy that learned its chops raiding Spanish treasure fleets, they had nothing left ... and everybody else had all the farms and factories. Spain never amounted to anything ever again.
Athens stopped being a quiet but spiritual and academic little town when it suddenly became possible to mine literally billions of dollars from a previously mined-out silver vein in Attica, only a few dozen miles from Athens, around 450 BCE. Over the next century, as Athens came more and more to depend on that money to subsidize everything under the sun, including food imported from Egypt, it became more and more fashionable to mock and make fun of the old-fashioned middle class hoplite farmers for their stubborn insistence on living the way the gods taught their ancestors to, for their adherence to Hesiod and Homer.
Then something even more disastrous happened: they won two wars in a row.
After the archaic dark age, the Persians expanded west into the then-wilderness of Turkey as the Ionian Greeks, mostly by now colonies of Athens, expanded eastward from the coast. Inevitably, the two sides met somewhere in the middle. Using local translators who spoke very little Farsi and very little Greek, the envoys from each side worked out a deal. Unfortunately, it became clear later that they only thought that they agreed on what the deal had been. What the Athenians took to be a peace ceremony, a treaty of non-interference, was interpreted by the Persians who asked for the ceremony as the total surrender of the entire Greek-speaking world to the Persian Empire. So when Persian tax collectors showed up on the Turkish coast, the Greeks threw them out. When they returned with an army, the Athenians counter-attacked and burned the Persian regional capital. Eventually the Persians responded by raising the largest army the world had ever seen. They marched across Turkey, across Macedonia, and all the way down the Greek peninsula. Until they hit Sparta, they met only token resistance, and a lot of abject surrender. When they hit the border of Sparta, the Spartans put up a brave but entirely futile fight at the battle of Thermopylae.
Then an honest-to-god miracle occurred. The Athenian assembly met to decide what to do: surrender, fight for the whole city, retreat to the old Acropolis fort and stage a last stand there, or evacuate by sea and hope to find a new place to live elsewhere. Someone rose up to say something really dumb. No, really, it was really dumb. What he obviously meant to suggest was that the Athenians reinforce the outer city wall with a wooden fence, a palisade, as if there was enough wood in all of Attica to do it or enough time to build it or for that matter, as if the Persians would have been slowed down for even 10 minutes by a wooden fence. But when he opened his mouth, a god spoke through him, and what came out was that Athens would not be saved by a wall of stone, but by a wooden wall. Still sounds dumb, but the oracle flew straight to the hearts of every man there, and they all knew what the gods wanted them to do: abandon the city and retreat to the wooden ships of the Athenian fleet, but instead of evacuating, stay and stage a naval ambush. It worked brilliantly, beautifully, beyond any reasonable human expectation, and at the Battle of Salamis this tiny little fairly-poor town completely destroyed the wealthiest and mightiest army the world had ever known.
It was a disaster. Why? Because they learned the wrong lesson from it. Instead of remembering that they had been saved by a god, they learned that the Athenian people were the mightiest on earth, and that when the assembly votes for something, even the gods themselves have to give it to them.
From there, it was all down hill. Instead of sending the soldiers home to rebuild their farms, Athens kept a large permanent navy and marine heavy infantry on duty from then on. Worse, practically the first thing they used that army for was to loot the treasury of the temple of Delian Apollo! They also used it to collect tribute from their colonies and former allies at sword point. When the rest of the Greek-speaking world rose up against them for this in the Peloponnesian War, they even managed to hold the Spartans and the Thebans and the Corinthians at bay.
In the middle of the Peloponnesian War, there were a couple of years when all of Athens moved within the city walls. They abandoned their farms altogether to the Spartans' superior infantry forces. Rather than coming out to fight, they simply kept importing food from Egypt, and waited for the Spartans to starve, give up, and go home. Instead of fighting the Spartan army at their gates, they sent their marine infantry out the back way by sea to raid the mostly-defenseless Spartan coastline, ripping up vines and burning sacred olive groves. Almost as soon as that fleet came back, a horrible plague of hemorrhagic fever broke out inside the city. They could have taken it as a warning that siege warfare wasn't working for them. They should have taken it as a punishment from the gods for hubris, for having looted the treasury at Delos, and for having burned sacred olive groves. But no, the orators were still flattering the voters that they were entitled to anything they voted for, and were guilty of no impiety. So the people concluded that the gods were no longer protecting virtue, and would therefore no longer punish vice. They learned the wrong lesson, again. It was another disastrous victory.
And when the Peloponnesian War was over, the Athenian assembly let themselves be flattered into believing that if the Persians couldn't defeat them and the Spartans couldn't defeat them, then nobody could. So they came up with an even more hubristic scheme: rather than buy food from Egypt, they would send the Athenian fleet to conquer the entire Egyptian empire. The fleet got as far as the city of Syracuse on the island of Sicily. Going the wrong way? Not exactly. To the Athenians, it seemed obvious to start by conquering Syracuse, because Syracuse had a huge fleet, a large army, and an unconquerable natural fort. They thought it would make a great addition to the Athenian military, and a great base from which to launch attacks on Africa. Somehow it didn't occur to them what "huge fleet, large army, and unconquerable natural fort" was going to mean. Why would they? They beat the Persians and the Spartans, didn't they?
The Syracusans did to the Athenians what the Athenians had done to the Persians, only more so. Hardly any adult Athenian men survived. In the resulting chaos, neither did the democracy, which was overthrown by a coup d'etat of wealthy aristocrats, the Thirty Tyrants.
The Greeks were warned by the gods at the very beginning. They knew to watch out for people who won huge windfall profits, but it never occurred to them what to do when a whole society reaps an unearned windfall profit. They originally knew to fear flattery, especially any demagogue who flatters the voters. They knew to fear hubris. They were warned to eschew impiety. They knew that they were at their strongest, and at their most free, when they were a nation of middle class farmers and small businessmen who kept themselves in shape, were ready to be called up to fight for their city, but even readier when the war was over to return to their farms and businesses. They should have known that a large standing army is nothing more than a great and powerful temptation to any slick-talking orator who might flatter the voters into letting him use that army for impiety and hubris. But after a hundred years of free money, they chose the impious and hubristic path of conquest and permanent war.
The Macedonian army, led by young Alexander's father King Philip of Macedon, came south to "rescue" the Athenians from the Thirty Tyrants. They never left. Well, they left when the Macedonian empire itself disintegrated after the death of Alexander, and even worse barbarians from Rome swept up the pieces. But the Romans slid into monotheistic military dictatorship. After that, the Romans were overrun by barbarians even worse than the Romans, bent on destroying civilization itself, and freedom and democracy and literacy and the last remnants of Hellenic religion went down into the dark. And Greece has never really amounted to anything ever again.