Later in the Classical period , the leagues would become fewer and larger , be dominated by one city ( particularly Athens , Sparta and Thebes ) ; and often `` poleis '' would be compelled to join under threat of war ( or as part of a peace treaty ) .
Later , in the Classical period , the leagues were fewer and larger , and dominated by one city ( particularly Athens , Sparta and Thebes ) . Often cities would be compelled to join under threat of war ( or as part of a peace treaty ) .