The Delian League of a couple of hundred Greek cities was formed under the leadership of Athens half-way through the Persian War to prosecute the defence against Persia - the war went on for another twenty years.
Athens.
Themistocles..
He was a prominent leader in Athens, and commanded the Athenian fleet which formed part of the Greek fleet which opposed the Persian invasion.
In the first part, Miletus. In the second part Sparta. In the third part, Athens.
It did not. The Persian Wars began in 499 BCE when the Greek city-states of Asia Minor revolted against Persian rule. Athens became involved when it sent an expedition to assist those cities.
Persian
In the later stage of the Persian War, Athens lled an anti-Persian league after Sparta retired from the leadership to handle its own sever internal problems. When peace was arranged with Persia, Athens continued to collect the financial contributions from the Greek cities of the Delian League, moved the treasury from Delos to Athens, and spent the money on itself and maintaining its fleet which it used to extort the money from the League members. The League was thus effectively converted to an empire of Athens. Athens became overconfident and interfered in the affairs of the Peloponnesian League led by Sparta, and this led to the eloponnesian War.
Yes
After the Persian War, Athens seized the opportunity to convert the Delian League, which it had led against the Persian Empire, into an empire of its own, and continued to collect the war funds by force to spend on itself - buildings, putting half its men on the public payroll, promoting cultural activities.
It led to Athens converting the Delian League of cities it led into an empire of its own, and becoming overconfident, getting into a devastating 27-year war with the Peloponnesian League. It lost and was stripped of its empire and became a second rate power.
Because the Persian army wanted to destroy individual Greek poli, so Athens convinced other poli to combine forces with them and make a league or an alliance in order to attack the Persian army and eventually win.
Sparta: Eurybiades and Pausanias. Athens: Miltiades. Themistocles, Xanthippos. Cimon