Long before the Justice League, there was the Chalkidian League. The two really had nothing to do with each other, save for the “League” at the end. Back then, it was in fashion for Greek cities to band together in leagues. Sometimes, membership was involuntary – somewhat like union membership.
During the time of Philip II, there were three major players in the area. The first was Macedon under Philip. The second was Athens, who had their paws everywhere, and the third was the Chalkidian League.
A large portion of the growth of Philip involved playing the Athenians and Chalkidians off of each other. The first target was Amphipolis. Due to their silver mines and the fact that it was the most in vogue city to have for the territory-grabbing king of the day, everyone wanted it. So, Philip II took the city with the promise of handing it over to Athens, but then he decided he rather liked the town, so he kept it.
To appease the Chalkidians, Philip took Potidae from Athens and handed it over to the Chalkidians. Nevertheless, all sides agreed to an everlasting peace, which is Greek terms meant they would mostly stop killing each other for a couple of years.
That ended in roughly 353 BCE, when to Philip‘s glee the Chalkidians entered into an alliance with Athens. This gave him the pretext for a major land grab by invading the Chalkidian League. Helpless against a superior military power, they crumbled bit by bit until Philip II took their capital Olynthos in 348 BCE.
This date was a major turning point for Philip, as he turned from a mostly Macedonian border focus to the East. With the topping of the Chalkidian League, Philip was now the major power in Greece. This allowed him to look along Greece’s borders, where he set his eyes on the Achaemenid Empire.
Chalkidian League formed.
The Peace of Nikias between Athens and Sparta is signed after the deaths of Cleon and Brasidas. They agree to break up the Chalkidian League, but this is not done.
Amyntas III of Macedon transfers territory to Olynthos of the Chalkidian League.
Amyntas III appeals to the Spartans against the Chalkidian League. Akanthos, Argilos, and Stageira also claim that membership was forced upon them. Potidaia is separated from the League.
The Chalkidian League become subject allies of Sparta.
The Chalkidian League leave Sparta and join and alliance with Athens, but that soon falls out over ownership of Amphipolis.