Why in the 5th century BC the power of Athens increased in comparison with other Greek city-states?

Athens won a series of brilliant victories over the Persians and this increased their power and ensured a leading role in the Union. Representatives of a number of Greek cities on the island of Dalos entered into an alliance called the Dalos military alliance. A unified treasury was established, and a unified ground force and navy were created. The affairs of the Union were managed by a council of representatives from all cities – members of the Union. Very soon the supremacy of Athens in this Union was designated, therefore it received the name of the First Athenian Maritime Union.
Gradually, the participation of other cities in the affairs of the Union was limited to making a certain contribution. These funds were transferred to the Athenians, who formed the land force and navy. Athens maintained democratic order in the allied policies. In the cities that were part of the Athens Maritime Union, there were the same systems of government.