The correct answer to this open question is the following.
Imagine the place where you live was a Greek poli. What other surrounding towns might join your poli in a league?
Greeks poli were areas or towns that oftentimes were surrounded by big walls that protected the poli inhabitants. In history, we know these places as "city-states." The most important city-states in ancient Greece were Athens and Sparta.
So I imagine myself living in the city-state of Greece because I like the cultural aspect of Athens and its philosophers like Socrates, Plato, and Aristoteles.
That is why I would invite other close villages, neighborhoods, and towns to join my polis to have better trade agreements and educational exchange. Yes, teachers from my poli could go and teach other close polis and strengthen our relationships until we are ready to form a league of city-states, based on cooperation.
