The animosity toward them on par grew is ascertained that States that passed for their protection (rear Delian League) were taxes that were used for the maintenance of its already powerful army and finance large public works. The problem grew more with the arrogance of the Athenians, especially of Pericles. Even, some time later, made effective the famous Megarian Decree, by which merchants of that city-state (ally of Sparta), could not navigate or in its waters, and used the ports of her Empire. The mandate was savagely injurious to the economy of Megara, so had to resort to Sparta to end that fight for their rights. After consulting with its allies, Sparta sent a delegation to Athens to demand the revocation of the measure and the dismissal of the Alcmaeonid family of power, including Pericles. The proposal outraged the Athenians, who had indicated that they would only accept the measure if Sparta It ended with the expulsion of foreigners in their territories, something inconceivable for closed Spartan society. Pericles was still more insolent: asked Sparta to recognize the autonomy of the different city-states that formed the Peloponnesian League, which was taken at Sparta as an open provocation. Archidamus II, King of Sparta, named a second and final delegation who asked Athenians to obey their previous demands.
It was all in vain. They could not even enter the Acropolis. The final spark that ignited the peninsula was a revolt of the island of Corcyra against their metropolis Corinth. As Athens sediciosamente became part of Corcyra and the Corinthians were subordinates of Sparta, they decided the war against Athens, thus breaking the famous 30 years peace signed in 446 BC For the first time, all Greek States would participate in a same conflict, giving him a much more atrocious nuance to the conflict. Invasion of Attica (431 a. c 421 )