History of the Peloponnesian War

Now not many years after this happened the matters before related, of the Corcyraeans and the Potidaeans and whatsoever other intervenient pretext of this war.

These things done by the Grecians one against another or against the barbarians came to pass all within the compass of fifty years at most, from the time of the departure of 118erxes to the beginning of this present war. In which time the Athenians both assured their government over the confederates and also much enlarged their own particular wealth. This the Lacedaemonians saw and opposed not, save now and then a little, but, as men that had ever before been slow to war without necessity and also for that they were hindered sometimes with domestic war, for the most part of the time stirred not against them; till now at last, when the power of the Athenians was advanced manifestly indeed and that they had done injury to their confederates, they could forbear no longer, but thought it necessary to go in hand with the war with all diligence and to pull down, if they could, the Athenian greatness. For which purpose it was by the Lacedaemonians themselves decreed that the peace was broken and that the Athenians had done unjustly;

and also having sent to Delphi and enquired of Apollo whether they should have the better in the war or not, they received, as it is reported, this answer: That if they warred with their whole power, they should have victory and that himself would be on their side, both called and uncalled.