Cause: Before this period, almost the whole of Greece stood up and fight the Persians together, and as they succeed, the two strongest city-states (Athens and Sparta) formed the Delian League with other city-states, and this league formed because Greece fears that a strong enemy, such as Persia, will attack Greece again. Every city-state in this League will put money in this league for the strong city-states to build strong armies and ships, while when they are attacked, the whole of Greece will use the army to support them. However, later through time, Athens decides to use the money for themselves, instead of the whole of Greece. Athens used this money to build new buildings and decorate their city. Sparta, the other city states fear that the Athens will become too strong using the money, so the other city states attacked Athens with Sparta as the leader. After the war broke up, the Athens decide to call all the Athenians to escape into the city state, and everyone defend from others attack.