While the Greek city-states had an approximate balance of power, they thrived and flourished. Wars were typically small and minor, consisting of a few battles, which, while often deadly to both sides, tended to leave cities and civilians unharmed.
Beginning just before the Peloponnesian War, however, a series of city-states felt strong enough to contest with each other for the hegemony of Hellas, and their ambitions brought destruction and war to Greece. Eventually, the Greeks were so weakened by their internecine wars that they fell easy prey to the Macedonians.
Had they instead been satisfied with the balance of power, rather than giving in to overweening pride and glory lust, how much more free and happy would they have remained.