Remember what happened in Messenia some years ago [462 BC]:
The Spartans tried to capture the stronghold of Mount Ithome in Messenia, where a large force of rebellious helots [enslaved Messenians] had taken refuge. The Spartans asked their allies from the Persian Wars, including the Athenians who were skilled in siege operations, to help. Our leader Cimon sought the support of Athens’ citizens to provide help for Sparta. Although his political opponent Ephialtes maintained that Sparta was Athens’ rival for power and should be left to look after itself, Cimon’s view prevailed. Cimon then led 4,000 hoplites to Mount Ithome.
After an attempt to storm Mount Ithome failed, the Spartans started to distrust the Athenians amid growing concerns that they might take the side of the helots and attempt some political changes. Keeping their other allies, the Spartans sent Cimon and his men home. This offensive rebuff caused the collapse of Cimon’s popularity at Athens, where outrage over the dismissal swung Athenian opinion towards Ephialtes’ views. They made an alliance with Sparta’s enemy Argos, and Ephialtes passed a law in the Athenian ecclesia (assembly) which reformed the conservative Areopagus, limiting its power to judging cases of homicide and religious crimes.