History of the Peloponnesian War

Amongst other causes of revolts the principal was their failing to bring in their tribute and galleys and their refusing (when they did so) to follow the wars. For the Athenians exacted strictly and were grievous to them by imposing a necessity of toil which they were neither accustomed nor willing to undergo.

They were also otherwise not so gentle in their government as they had been, nor followed the war upon equal terms, and could easily bring back to their subjection such as should revolt.

And of this the confederates themselves were the causes. For through this refusal to accompany the army the most of them, to the end they might stay at home, were ordered to excuse their galleys with money, as much as it came to, by which means the navy of the Athenians was increased at the cost of their confederates, and themselves unprovided and without means to make war in case they should revolt.