Philip of Macedon ascended the throne of Macedon in his late twenties. He had found himself regent, that is, the individual in charge of the kingdom because the king was only an infant. As regent, he promptly overthrew his infant nephew, the king, and crowned himself king in 359 BC. In his early twenties, however, he had been a Macedonian hostage living in Thebes during the heyday of the Theban hegemony. Political hostages generally lived a good life, they were simply kept in order that they may be executed if hostilities commenced between the government the hostage came from and the government that held him (or her). Philip lived a good life in Thebes and was well-integrated into the politics and military. He grew to think of himself as a Greek rather than as a Macedonian, but he also learned Greek politics and Greek military strategy. Philip had learned to be a general.
When he assumed the throne of Macedon, he promptly pacified all the European tribes to his north, seized gold and silver mines by conquering the city of Amphipolis to his south, and began to build new cities and large standing armies.
He then turned his eyes to the south in 349 BC and began to systematically conquer all the Greek cities; after a great victory against Athens and its allies in 338 BC, Philip found himself in control of all Greece (except Sparta). Philip promptly went to work at securing his power in Greece, building garrisons at Corinth, Thebes, and Chalcis; in 338 BC, he created the Federal League of Corinth. Ostensibly an alliance of free city-states, Philip was its ruler and for all practical purposes had become king of Greece. The independent city-state, the polis, had ceased to exist. But Philip wasn't finished. The Persian Wars still festered in the Greek memory, and the Spartan invasion of Persia in 379 BC showed Philip that it was possible to defeat the mightiest empire known to humanity. So in 337, Philip announced the the League would attack Persia as revenge for the wars, and in 336 he stood poised to prosecute his mighty invasion of the Persian Empire, but an assassin's sword ended his great campaign. It should've ended the brief Macedonian control of Greece; but Philip's twenty-one year old son stepped into his father's shoes and became the conqueror of the world.