The History of the Peloponnesian War is a historical account of the Peloponnesian War, which was fought between the Peloponnesian League and the Delian League. It was written by Thucydides, an Athenian historian who also happened to serve as an Athenian general during the war.

THUCYDIDES, an Athenian, wrote the history of the war in which the Peloponnesians and the Athenians fought against one another. He began to write when they first took up arms, believing that it would be great and memorable above any previous war. For he argued that both states were then at the full height of their military power, and he saw the rest of the Hellenes either siding or intending to side with one or other of them. No movement ever stirred Hellas more deeply than this; it was shared by many of the Barbarians, and might be said even to affect the world at large. The character of the events which preceded, whether immediately or in more remote antiquity, owing to the lapse of time cannot be made out with certainty. But, judging from the evidence which I am able to trust after most careful enquiry, I should imagine that former ages were not great either in their wars or in anything else.
The country which is now called Hellas was not regularly settled in ancient times. The people were migratory, and readily left their homes whenever they were overpowered by numbers. There was no commerce, and they could not safely hold intercourse with one another either by land or sea. The several tribes cultivated their own soil just enough to obtain a maintenance from it. But they had no accumulations of wealth and did not plant the ground; for, being without walls, they were never sure that an invader might not come and despoil them. Living in this manner and knowing that they could anywhere obtain a bare subsistence, they were always ready to migrate; so that they had neither great cities nor any considerable resources. The richest districts were most constantly changing their inhabitants; for example, the countries which are now called Thessaly and Boeotia, the greater part of the Peloponnesus with the exception of Arcadia, and all the best parts of Hellas. For the productiveness of the land increased the power of individuals; this in turn was a source of quarrels by which communities were ruined, while at the same time they were more exposed to attacks from without. Certainly Attica, of which the soil was poor and thin, enjoyed a long freedom from civil strife, and therefore retained its original inhabitants. And a striking confirmation of my argument is afforded by the fact that Attica through immigration increased in population more than any other region. For the leading men of Hellas, when driven out of their own country by war or revolution, sought an asylum at Athens; and from the very earliest times, being admitted to rights of citizenship, so greatly increased the number of inhabitants that Attica became incapable of containing them, and was at last obliged to send out colonies to Ionia.