12. If now we consider the events which have been briefly traced in the foregoing pages, it will be perceived, that the principle on which the Lacedæmonians constantly acted was one of self-defence, of restoring what had been lost, or preserving what was threatened with danger; whereas the Athenians were always aiming at attack or conquest, or the change of existing institutions. While the Spartans during this period, even after the greatest victories, did not conquer a foot of land, subjugate one independent state, or destroy one existing institution; the Athenians, for a longer or for a shorter time, reduced large tracts of country under their dominion, extended their alliance (as it was called) on all sides, and respected no connexion sanctioned by nature, descent, or antiquity, when it came in conflict with their plans of empire. But the astonishing energy of the Athenian people, which from one point kept the whole of Greece in constant vibration, almost paralysed Sparta; the natural slowness of that state became more and more apparent: which having been, as it were, violently transplanted into a strange region, only began by degrees to comprehend the policy of Athens.
But when Athens saw the Peloponnesian confederacy again established, and as she could not, on account of the truce, attack it directly, she looked to the colonial law, which rested rather on hereditary feelings than on positive institution, for an opportunity of an indirect attack. This was soon found in the defensive treaty with Corcyra, which state was engaged with its mother country Corinth in a war, according to ancient Greek principles, wholly unlawful and unjust. Besides this, however, it was an actual breach of the thirty years’ truce.(842) And the same principles were expressed in the demand that Potidæa should, for the sake of the Athenian confederacy, give up its original connexion with the parent state. In both these cases it is manifest that the maxims of the Athenian policy were directly at variance with the general feeling of justice entertained by the Greeks, and especially with the respect for affinity of blood; and this fundamental difference was the true cause of the Peloponnesian war.