Preceding analyses of the Peloponnesian War omit certain facts, such as that the war wasn’t won by the Spartans and their associated Greek allies until the (non-Greek) superpower of the age, the Persian Empire — far from vanquished as a result of the Greco-Persian wars earlier in the (5th) century — intervened in the conflict, throwing its enormous weight behind the Spartans et al. Thus, Greek disunity was the enabling factor in yet another disastrous interference by the Persians in Greek affairs, while the Spartans and their allies were, arguably, traitors to that Greek cause.

Second, the war wasn’t lost by Athens so much because of those external factors, nor due to the plague, disastrous though it was, but as a result of the fact that Athens, brilliant though it was, was a miserable failure in finding a political, probably federal solution to transforming the original Delian League into the “Athenian Empire” — in a way that would satisfy its constituent cities/allies so that the enlarged state had cohesive staying power, like America from the thirteen colonies.

Lacking such a federal structure, the Athenians could not resist tampering in the internal affairs of their subject cities, interference which the least of them (not to speak of greatest) bitterly resented — with the result that, when push came to shove, the Athenian Empire simply fell apart.

Compare that experience with that of Rome, which during the Republic period granted to its Italian member cities rights of autonomy and self-government, which policy was later extended Empire-wide — with the result that Rome’s allies went to war with it (in the so-called Social War of 90-89 BC) in order not to escape Rome but rather force her to admit them into the Roman state! Which they won — or rather, lost, after which they were admitted into full, autonomous membership in the Roman Republican state.

Note the different lifetimes of the Athenian vs. Roman Empires — the Athenian disappearing in a few decades, the Roman the longest-lived state in history.