History of the Peloponnesian War

The causes why they brake the same and their quarrels I have therefore set down first, because no man should be to seek from what ground so great a war amongst the Grecians could arise.

And the truest quarrel, though least in speech, I conceive to be the growth of the Athenian power, which putting the Lacedaemonians into fear necessitated the war. But the causes of the breach of the league publicly voiced were these.