PBS
Pbs: Why Did Greece Develop City States?
This site from PBS gives three explanations for the development of city-states in ancient Greece.
Ducksters
Ducksters: Ancient Greece for Kids: Greek City States
A site dedicated to information about the city-states of Ancient Greece. Study the powerful cities such as Corinth, Thebes, Argos, and Rhodes.
Tufts University
Perseus: The Greek City States and Religious Festivals
Discusses the difference between modern and ancient Greek Olympic games, and goes into depth about the religious festivals that took place. Additional links to related material.
World History Encyclopedia
World History Encyclopedia: Achaean League
Illustrated encyclopedia entry on the Achaean League, a federation of Greek city-states during the 3rd and 2nd centuries BCE. Site includes timeline, maps, photos and bibliography.
Ducksters
Ducksters: Ancient Greece for Kids: Persian Wars
A website about the Persians Wars of Ancient Greece fought between Persia and the Greek city-states.