Why did the greek tyranny lose power?

At the end of the Classical period, around 360 B.C., the Greek city-states were weak and disorganized from two centuries of warfare. (First the Athenians fought with the Persians; then the Spartans fought with the Athenians; then the Spartans and the Athenians fought with one another and with the Thebans and the Persians.) All this fighting made it easy for another, previously unexceptional city-state to rise to power.