Final answer:
Philip II unified Greece through military dominance, establishing the League of Corinth after the Battle of Chaeronea, and planning a collective retaliation against Persia to maintain unity.
Step-by-step explanation:
King Philip II of Macedon united Greece through a combination of military conquest, tactical innovation, and strategic diplomacy. By defeating rival factions and securing control over territories rich with resources, Philip was able to expand his military prowess. His army was a formidable force, with a restructured phalanx and an elite cavalry that pledged loyalty directly to him. Noteworthy is the Battle of Chaeronea in 338 BCE, where Philip's forces crushed the combined armies of Athens and Thebes. Afterward, he persuaded the Greek city-states to join his League of Corinth, unifying them under his leadership with the agenda of launching a campaign against the Persia.
Philip also addressed economic necessities by looting and seizing lands, a strategy that kept his army's loyalty through material gain. Moreover, as a skilled statesman, he managed Greece by appealing to the shared cultural heritage and the idea of a collective retaliation against Persia. Though his rule was characterized by Macedonian hegemony, it sowed the seeds for his son Alexander the Great's further exploits.