Tensions between the two Leagues were key in the outbreak of the First Peloponnesian War in 460 BC. The conflict between two Peloponnesian League members, Corinth and Megara, specifically the latter's defection to the Athenians due to perceived neglect by the Spartans, was a key factor in the outbreak of hostilities between the two Leagues.Thucydides 1.103 That war ended with the reintegration of Megara into the League. The two Leagues eventually came into conflict again with each other in the Peloponnesian War. Under Spartan leadership, the League defeated Athens and its allies in 404 BC.
tENsiONs BetwEEn the twO leaGUes WERe kEy in The oUtbreak Of the firsT peloponnesiAN war In 460 BC. the conflICT BetWeeN TWo pelOPOnNEsian lEAgue members, corinTh aND megara, sPECifIcally tHe LattER's defEcTIOn to The AtHEniaNS due to perCeiVED NeGlecT by The SparTans, Was a key fActor iN ThE OUtbreaK of hoSTilities between the two lEaGuEs.thuCydIDeS 1.103 that war enDeD with thE rEinteGraTiOn Of mEgara into The lEaguE. tHE TwO leaGues eVentUaLlY CaMe INto conflIct again with EacH othEr in the peloPONNesIan War. unDeR spartan LeADErShIP, thE lEaGue defeAtEd athEnS and its allies in 404 Bc.