Why did greek city-states form the delian league?

The Delian League, founded in 478 BC, was an association of Greek city-states, members numbering between 150 173, to 330 under the leadership of Athens, whose purpose was to continue fighting the Persian Empire after the Greek victory in the Battle of Plataea at the end of the Second Persian invasion of Greece

How either some or all of the organisms in this activity are related to one another based

There is lots of evidence