Pericles made his first military excursions during the First Peloponnesian War, which was caused in part by Athens' alliance with Megara and Argos and the subsequent reaction of Sparta. In 454 BC he attacked Sicyon and Acarnania. He then unsuccessfully tried to conquer Oeniadea on the Corinthian gulf, before returning to Athens. In 451 BC, Cimon returned from exile and negotiated a five years' truce with Sparta after a proposal of Pericles, an event which indicates a shift in Pericles' political strategy. Pericles may have realized the importance of Cimon's contribution during the ongoing conflicts against the Peloponnesians and the Persians. Anthony J. Podlecki argues, however, that Pericles' alleged change of position was invented by ancient writers to support "a tendentious view of Pericles' shiftiness".