History of the Peloponnesian War

The Mantineans and their allies were the first to join them, through fear of the Lacedaemonians. For a part of Arcadia had been reduced to subjection by the Mantineans, while the war with the Athenians was still going on, and they thought that the Lacedaemonians, now that they had leisure, would not suffer them to retain their sovereignty. So they turned gladly to Argos, regarding it as a powerful state, one always at variance with the Lacedaemonians, and under a democratic form of government like themselves.

And when the Mantineans had revolted, the rest of the Peloponnesus also began to mutter that they must do the like, thinking that the Mantineans had changed sides because they possessed some superior knowledge. At the same time they were angry with the Lacedaemonians on other grounds, and especially because it was written in the treaty with Athens that it would be consistent with their oaths to add or take away whatever shall seem good to both states, that is, to the Lacedaemonians and Athenians.

For it was this article especially that was disturbing the Peloponnesus far and wide and causing suspicion that the Lacedaemonians wished in concert with the Athenians to reduce them all to slavery; for it would have been just, they thought, that the clause should have given the power to alter the articles to all the allies.

And so most of them were afraid and were eager on their own part also to make a separate alliance with the Argives.