With no formidable external threat, Greece returned to its normal instability and disputes between city-states on matters of self-interest. Temporary alliances changed until 30 years later Thebes defeated Sparta. It took Persian intervention to restrain the internecine wars, imposing the King's Peace.
Meanwhile Macedonia was growing in power.
The Greek city-states were never united, they formed temporary coalitions against each other, which came and went accorting to self-interest at any particular time.
After temporarily uniting against the Persian invasion (and even then there were Greek cities on the Persian side) they went back to business as usual the Persian threat was driven back.
The unifying force of the Delian League against Persia was converted into an empire by Athens, and when longer term peace was arranged with Persia in 449 BCE, Athens continued to collect the League funds to spend on itself and on maintaining naval supremacy. This led to the Peloponnesial League led by Sparta to counter Athenian dominance, and these two leagues slid into war.
Threat of annihilation by the Persian invasion
The Persians had to send half their army home as, with their sea supply line unprotected by their defeated fleet, they could not feed them in the oncoming winter. This left the way open for the Greek cities to unite and defeat them in the next spring.
Isabella I Queen of Castile and Leon helped unite Spain with her husband Ferdinand, King of Aragon. Together they defeated and expelled the Moors, and united Spain in 1492.
The Latins did not decided to unite and become Rome. Most Latin cities (not all of them) were annexed by Rome after their rebellion against Rome (which historians call the Latin War) was defeated.
They did not unite the Greeks - there was just a pause in their fighting each other while the games were on.
Most rational people think they fought them.
His father had a dream to unite the city-states. Shortly after he died so Alexander was his heir. Alexander took his father's dream and tried to unite the Greeks, the Persians, and the Macedonians. He failed
They needed to destroy the Persian fleet, which threatened the southern Greek cities and so forced them to stay at home defending their cities and so were unable to unite. So they set up a blocking force at the pass of Thermopylae to force the Persians to try to turn the position by sea, with their own fleet waiting to pounce in the narrow waters at Artemesion. Unfortunately for them, their fleet was defeated, so they withdrew the blocking force as no longer of use. The Spartan and hespian contingents remained to protect the withdrawal and were slaughtered.
The Persians who was led by Xerxes .
Threat of annihilation by the Persian invasion
The Persians had to send half their army home as, with their sea supply line unprotected by their defeated fleet, they could not feed them in the oncoming winter. This left the way open for the Greek cities to unite and defeat them in the next spring.
he surrendered to grant
The Greeks had to eliminate the Persian naval threat to their city-states in order for their armies could leave off defending them and unite to face the Persian army. They blocked the pass of Thermopylae to force the Persians to attempt to turn it by sea. The Greek fleet waited in the nearby channel to pounce. Unfortunately for them they lost the sea battle and the force of 7,000 holding Thermopylae was withdrawn. The Spartan and Thespian contingents stayed behind to cover the withdrawal and were killed. The Greeks tried again a Salamis and were succful, and their armies united the following summer to defeat the Persian army at Plataea.
Originally? To unite Greeks against the threat of the Persians. After the defeat of the Persians? To execute and maintain Athenian hegemony in the Aegean. Or to put the second point in another way, to give Athens the money to keep its fleet in place to enforce the annual collection of funds from the members, and spend the rest of the tribute on improving its own city and keep half its people on the public payroll.
Alexander sought to create an empire, and by subjugating and organizing the lands more native to him (although as a Macedonian, he was not quite considered "Greek" by the standards of the day) he created a strong foundation to the empire that would span across the known world.
The Greeks ware not a cohesive nation - there were hundred of independent Greek city-states in eastern Europe, Asia Minor and the Islands, almost continuously at war with each other. They bought off a group of these Greek cities onto their side, and had a large navy drawn from Phoenicia, the Asia Minor Greek cities and Egypt. This navy threatened the Greek cities with amphibious invasion so they y kept their armies at home defending their own city. It was only after the Greeks defeated the Persian navy at Salamis, and that threat was lifted, that the cities were prepared to send out their armies the following year to unite at Plataea for the decisive land battle.
The Life of Alexander the GreatIn 359 B.C., Philip II came to the throne in powerful Macedonia. He longed to unite Greece and Macedonia. Fearful of Philip's intentions, the Greeks formed a defensive alliance, but they were defeated. It was then that Philip passed the torch on to his son, Alexander.