In the beginning in 478 BC which league served as a protective group and a defensive league?

In 478 BC, the Delian League was established as a protective alliance among Greek city-states, primarily to defend against potential Persian invasions following the Persian Wars. Led by Athens, the league aimed to provide mutual military support and ensure the security of its member states. Over time, however, it evolved into an Athenian empire, with Athens exerting significant control over the league's operations and resources.