History of the Peloponnesian War

Now while there were other causes of revolts, the principal ones were the failures in bringing in the tribute or their quota of ships and, in some cases, refusal of military service; for the Athenians exacted the tribute strictly and gave offence by applying coercive measures to any who were unaccustomed or unwilling to bear the hardships of service.

And in some other respects, too, the Athenians were no longer equally agreeable as leaders; they would not take part in expeditions on terms of equality, and they found it easy to reduce those who revolted.

For all this the allies themselves were responsible; for most of them, on account of their aversion to military service, in order to avoid being away from home got themselves rated in sums of money instead of ships, which they should pay in as their proportionate contribution, and consequently the fleet of the Athenians was increased by the funds which they contributed, while they themselves, whenever they revolted, entered on the war without preparation and without experience.