The differences between Athens and Sparta eventually led to war between the two city-states. Known as the Peloponnesian War (431-404 B.C.), both Sparta and Athens gathered allies and fought on and off for decades because no single city-state was strong enough to conquer the others.
The whole of Hellas used once to carry arms, their habitations being unprotected, and their communication with each other unsafe; indeed, to wear arms was as much a part of everyday life with them as with the barbarians. And the fact that the people in these parts of Hellas are still living in the old way points to a time when the same mode of life was once equally common to all. The Athenians were the first to lay aside their weapons, and to adopt an easier and more luxurious mode of life. -Thucydides, The Peloponnesian War, (1910 translation by Richard Crawley)
With war came famine, plague, death, and misfortune. But war cannot kill ideas. Despite the eventual military surrender of Athens, Athenian thought spread throughout the region. After temporary setbacks, these notions only became more widely accepted and developed with the passing centuries.

License information: CC BY 4.0
MPAA: PG
Go to source: https://www.commonlit.org/texts/the-rise-of-greek-city-states-athens-versus-sparta