440 BC, when Athens's powerful ally Samos rebelled from its alliance with Athens. The rebels quickly secured the support of a Persian satrap, and Athens faced the prospect of revolts throughout its empire. The Spartans, whose intervention would have been the trigger for a massive war to determine the fate of the empire, called a congress of their allies to discuss the possibility of war with Athens. Sparta's powerful ally Corinth was notably opposed to intervention, and the congress voted against war with Athens. The Athenians crushed the revolt, and peace was maintained. The more immediate events that led to war involved Athens and Corinth. After a defeat by their colony of Corcyra, a sea power that was not allied to either Sparta or Athens, Corinth began to build an allied naval force. Alarmed, Corcyra sought alliance with Athens. Athens discussed with both Corcyra and Corinth, and made a defensive alliance with Corcyra. At the Battle of Sybota, a small contingent of Athenian ships played a critical role in preventing a Corinthian fleet from capturing Corcyra. In order to uphold the Thirty Years' Peace, the Athenians were instructed not to intervene in the battle unless it was clear that Corinth would invade Corcyra. However, the Athenian ships participated in the battle, and the arrival of additional Athenian triremes was enough to dissuade the Corinthians from exploiting their victory, thus sparing much of the routed Corcyrean and Athenian fleet. Following this, Athens instructed Potidaea in the peninsula of Chalkidiki, a tributary ally of Athens but a colony of Corinth, to tear down its walls, send hostages to Athens, dismiss the Corinthian magistrates from office, and refuse the magistrates that Corinth would send in the future. Outraged, the Corinthians encouraged Potidaea to revolt and assured them that they would ally with them should they revolt from Athens. During the subsequent Battle of Potidaea, the Corinthians unofficially aided Potidaea by sneaking contingents of men into the besieged city to help defend it. This directly violated the Thirty Years' Peace, which stipulated that the Delian League and the Peloponnesian League would respect each other's autonomy and internal affairs. A further provocation was Athens in 433/2 BC imposing trade sanctions on Megarian citizens (once more a Spartan ally after the First Peloponnesian War). It was alleged that the Megarians had desecrated the Hiera Orgas. These sanctions, known as the Megarian decree, were largely ignored by