The correct answer is the Delian League.
During the Persian wars, Athens and the city-states that rallied behind them became known as the Delian League.
Athens led the group of city-states and formed the Delian league in 478 BC. This way they were stronger to fight the invasion of the First Persian Empire. The name of the league stemmed from the Greek island of Delos. They used the strength of the Athenian navy to combat the Persians by sea.
