History of the Peloponnesian War

Ten years afterwards the barbarian returned with the armada for the subjugation of Hellas. In the face of this great danger the command of the confederate Hellenes was assumed by the Lacedaemonians in virtue of their superior power; and the Athenians having made up their minds to abandon their city, broke up their homes, threw themselves into their ships, and became a naval people. This coalition, after repulsing the barbarian, soon afterwards split into two sections, which included the Hellenes who had revolted from the king, as well as those who had aided him in the war. At the head of the one stood Athens, at the head of the other Lacedaemon, one the first naval, the other the first military power in Hellas.

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.

The policy of Lacedaemon was not to exact tribute from her allies, but merely to secure their subservience to her interests by establishing oligarchies among them; Athens, on the contrary, had by degrees deprived hers of their ships, and imposed instead contributions in money on all except Chios and Lesbos. Both found their resources for this war separately to exceed the sum of their strength when the alliance flourished intact.