Check this out from
the New Yorker.
The war that began in the spring of 431 represented what [was] rightly call[ed] "a fundamental departure" from [Athens'] tradition, not only in its scope, duration, and complexity but also in savagery and bitterness. After the Corinthian diplomatic crisis, ties between Athens and Sparta disintegrated. Hostilities began, one night early in 431, with a sneak attack on a small Athenian protectorate called Plataea. This sordid violation of the norms of Greek warfare set the tone for what was to come. As the conflict spread across many fronts, from the Hellespont to Sicily to the coast of Asia Minor, it began to seem frustratingly unwinnable. The result, Kagan emphasizes, was a cycle of cruelty and reprisal that ended in a "collapse in the habits, institutions, beliefs, and restraints that are the foundations of civilized life": schoolboys slaughtered in their classrooms by mercenaries, civilians murdered and enslaved en masse, supplicants dragged from (or burned at) altars, the war dead left to rot on the battlefield. In the end, the great standard-bearer of Greek civilization itself, Athens, collapsed. Bankrupt and imploding with civil strife after nearly three decades of fighting, it was finally defeated by an alliance of Sparta and Persia, the traditional enemy of the Greeks.