Greek Dark Ages
Immediately after the death of Alexander III the Great in 323 BCE, his empire fragmented into several splinters, with the Greek peninsula being ruled by Cassander, son of Alexander the Great's general, Antipater (Who had remained regent over all of Greece while Alexander had campaigned in the east). However, struggles for mastery over Greece proper came in the form of Antigonus of Anatolia (another general of Alexander's), who promised to liberate all of Greece if the Greek people supported him. After securing most of Greece and cementing the Antigonid dynasty of kings which would subsequently rule over most of Greece and Macedonia. However, city-states like Athens, Rhodes, and Sparta would remain mostly independent. Over the course of the next century, Macedon's rule over Greece would slowly begin to slip, with some Greek city-states (some backed by Ptolemaic Egypt - a fierce rival of Macedon in the post-Alexandrian War of the Successors) forming leagues that contested the Macedonian kingdom's mastery over Greece. A key example would be Athens, which sought many allies abroad (such as Egypt and the Attalid dynasty ruling the powerful state of Pergamum in Anatolia) to help gain independence from Macedon.
However, this volatile situation changed when Philip V (Philip the fifth) ascended to the Macedonian throne. The Macedonian king effectively brought an end to the conflicts between the leagues and Macedon, uniting most of Greece once again under Macedonian rule (except the cities of Athens, Rhodes, and Pergamum). All would not remain this way, as the growing power of Rome in the west threatened the very borders of Greece itself. Discontented with Macedonian rule, many of the Achaean cities (the Peloponnesian cities of southern Greece) turned to the Romans (who were widely proclaiming freedom for the Greek city states if they supported them against Macedon) for support against their Macedonian overlords and in response, Philip entered an alliance with the Republic of Carthage, Rome's great Mediterranean rival across the sea. The alliance was made while Carthaginian forces (led by the famous general Hannibal Barca) were handing the Romans a series of major military defeats both on and off their home territory of Italy. However, the alliance was mostly in name only, and neither side did much to benefit the other. This alliance, however, marked Macedon as Rome's target and when the Romans finally defeated the Carthaginians, they turned eastwards and fought the Macedonian Kingdom in a series of wars called the Macedonian Wars.
The turning point would be during the Second Macedonian War, where Philip V was decisively beaten at the Battle of Cynosephalae. While Rome had declared that it was fighting in the interest of Greek independence, the reality was that Rome now controlled the Greece, with Roman garrisons being placed in most Greek cities. The defeat of Macedon in this war was necessary as Rome recognized the serious threat that the Seleucid Empire (a successor kingdom that broke off from part of Alexander's empire - it was arguably the largest piece of the empire, spanning most of Alexander's eastern territories and the most powerful at the time of Rome's ascension) posed to the Roman Republic (the Romans wanted to knock out Macedon, before they could join the Seleucids against the Romans). Over the course of the next century, Macedonian and other Greek leaders would attempt uprisings which would ultimately fail, with the final blow coming when Rome crushed the Greek city-states for rebelling against Roman control and for allying with King Mithradates of Pontus. Greece would not be formally annexed as a Roman territory (it had up to now been a protectorate of Rome) until the time of the newly emerging Roman empire under its first emperor, Augustus. Greece would be organized into the Roman province of Achaea.