History of the Peloponnesian War

For a short time the league held together, till the Lacedaemonians and Athenians quarrelled, and made war upon each other with their allies, a duel into which all the Hellenes sooner or later were drawn, though some might at first remain neutral. So that the whole period from the Median war to this, with some peaceful intervals, was spent by each power in war, either with its rival, or with its own revolted allies, and consequently afforded them constant practice in military matters, and that experience which is learnt in the school of danger.