We hope that you, instead of thinking to influence us by saying that you did not join the Lacedaemonians, although their colonists, or that you have … - Thucydides

the strong do what they can and the weak suffer what they must.

..since you know as well as we do that right, as the world goes, is only in question between equals in power, while the strong do what they can and the weak suffer what they must.

But his (Pericles’) successors were more on an equality with one another, and, each one struggling to be first himself, they were ready to sacrifice the whole conduct of affairs to the whims of the people.

Such weakness in a great and imperial city led to many errors, of which the greatest was the Sicilian expedition; not that the Athenians miscalculated their enemy's power, but they themselves, instead of consulting for the interests of the expedition which they had sent out, were occupied in intriguing against one another for the leadership of the democracy, and not only hampered the operations of the army, but became embroiled, for the first time, at home.

And yet after they had lost in the Sicilian expedition the greater part of their fleet and army, and were now distracted by revolution, still they held out three years not only against their former enemies, but against the Sicilians who had combined with them, and against most of their own allies who had risen in revolt. Even when Cyrus the son of the King joined in the war and supplied the Peloponnesian fleet with money, they continued to resist, and were at last overthrown, not by their enemies, but by themselves and their own internal dissensions.

(Book 2 Chapter 65.10-12)

At times Thucydides may be clearly mistaken in both detail and interpretation, but the extent of his accuracy and analysis astounds in a world where travel was difficult, written sources rarely available, and the physical obstacles to the writing of history substantial.

In times of peace and prosperity cities and individuals alike follow higher standards, because they are not forced into a situation where they have to do what they do not want to do. But war is a stern teacher; in depriving them of the power of easily satisfying their daily wants, it brings most people’s minds down to the level of their actual circumstances.