What was the Athenian Empire in disguise?

Answer 1

The anti-Persian alliance formed after the 479 BCE defeat of the Xerxes invasion.

Athens took over leadership of this alliance and assessed contributions from the cities, which could be paid in warships or money. Most cities preferred the latter, and so Athens had an unchallenged superior navy, which was used to enforce the contributions. So the character of the alliance changed from a free association for defence to an empire paying tribute. Pericles is recorded as openly saying it was an empire.