The reason why Spartans won the Peloponnesian War is first, their army. At a very young Age Young Spartan boys were taught for the battle field thus having a immense capability of fighting compared to the Athens. As Athens would choose poetry, and other subjects instead of Spartan's culture, which is training their people to fight. Another reason was the strategy of the Athens, who has very poor strategy compared to Spartan's experience in battle.
