Gelo

A military coalition of Greek city-states led by Sparta and known as the Peloponnesian League, also called the Spartan Alliance, is a major force in Greek affairs, forming the nucleus of resistance to the Persian invasions.

League policy, usually decisions on questions of war, peace, or alliance, is determined by federal congresses, summoned by the Spartans when they think fit; each member state has one vote.

A general Greek league against Persia is formed in 481.

Quarrels like that between Athens and Aegina must be set aside and help sought from distant or colonial Greeks such as the Cretans, Syracusans, and Corcyrans, whose extraordinarily large fleet of sixty ships (possibly developed against Adriatic piracy but also—surely—against Corinth) will be a prime asset.

Corcyra, however, waits on events, and Crete stays out altogether, while Syracuse and Sicily, now under the tyranny of Gelo, generally have barbarian enemies of their own to cope with, the Carthaginians.

Command of the army is given to Sparta, …

…that of the navy to Athens.

The combined Greek fleet, which, even without western Greek help, numbers about three hundred and fifty vessels, is thus only about one-third the size of the Persian fleet.

Greek unity, though impressive, is not complete; …

…conspicuous among the “Medizers” is Thebes, whose hostility to Athens over mutual interest in the Plataea district leads to Theban collaboration with Persia, while …

…the neutrality maintained by Argos amounts, in Herodotus's view at least, to Medism.