Greek city states?

The Greek city-states were independent cities ruled by their own kings. For example, in ancient Sparta, a king ruled, and in Athens, the People’s Assembly was at the head. Also, the Greek polis were often at odds with each other in order to expand their influence. True, there were times when they united to fight a common enemy. As it happened during the period of the Greco-Persian wars in the 5th century BC. Then a huge army of Persians invaded Greece, and if the Greeks had not united, then Xerxes would have captured all the Greek cities.