History of the Peloponnesian War

Now there were other reasons for the revolts, but the principal were arrears of tribute and ships, and failing (if any did so) in military service: for the Athenians strictly exacted these things, and were offensive by usingcompulsion to men who were neither accustomed nor willing to do hard work.

In some other respects also they were no longer liked in their government, as they had been; and while they did not join in the service on an equal footing, at the same time it was easy for them to bring to subjection those who revolted.