Alexander’s Macedonia was a late developer, on the periphery of the Greek city-states:
Moreover, it was essentially an inland state, not a maritime power; its strength was its extensive agricultural lands, and its access to the plains with their horses and pastoralists.
To the south was the Greek peninsula, broken by mountains and inlets of the sea, a land of walled city-states. Rarely able to expand their land frontiers, they engaged in maritime expeditions, lived by trade and booty, and by sending out colonies around the Mediterranean littoral. The same pattern held on the eastern shore of the Aegean Sea. The result was that Greek city-states could rarely conquer each other. Some did become more prestigious than others, and forced the others into coalitions. This Athens did when it became the center for the massed fleet that repelled the Persian invasions, subsequently becoming a quasi-empire in their own right collecting duties to support the fleet.* But as land powers, the city-states were essentially deadlocked.
*The cultural prestige of Athens starts at this time. Before 460 BC, Greek poets, philosophers, mathematicians and scientists were spread all over; they concentrate in Athens when it becomes the biggest, richest, and most powerful city. The cultural fame of Athens is a result of its geopolitical rise. It became the place where all the culture-producing networks came together, and remained the place for centuries as the leading networks reproduced themselves.
Simultaneously, the Persian empire had reached the limits of its logistics and its administrative capacity for holding itself together. There was no longer any real danger of Persian expansion into Greece; it was just another player in the multi-player situation. The Persian invasions were in 490 and 480-79 BC; both failed because the Persians could not sustain an army across the water against navies equal to what they could raise. The last Persian forces on the European side of the straits were thrown out by 465 BC. The Athenians played up the Persian threat as the basis of their own power, down to about 400, when they lost a long domestic war of coalitions.**
**The defeat of Athens by Sparta was not the end of democracy, or anything of the sort. Greek history is dominated by Athenian propaganda, because the great historians of this period — Herodotus, Thucydides, Xenophon — were all Athenians or sympathizers. It helped that Socrates and Plato were Athenians, and their dialogues make the Athenian scene come alive, as do the comedies of Aristophanes. That is why we moderns, styling ourselves inheritors to Greek democracy and science, have such a narrow Athenian peep-hole view into the history of Greece.
The period from the 390s BC down to the rise of Macedonia in the 340s, is one where numerous powers and coalitions vie with each other. Sparta, Athens, Thebes, the Boeotian league, the Phocians, all have a try at becoming hegemon. The term itself is revealing: it means, not conqueror or overlord, but leader, preponderant influence. The situation has settled into a multi-sided, unstably ongoing set of conflicts.
Outside the deadlocked heartland, there was opportunity for a marchland state to grow. Since the major players had their attention locked in, a peripheral actor could grow in its own environment, becoming dominant through a local elimination contest. This is what the Macedonian kingdom did. First its settled agricultural zone expanded inland to incorporate nearby hill tribes, recruiting them into a victoriously expanding army; then growing north and east into Thrace (what is now Bulgaria and European Turkey) by beating barbarian kings and weak tribal coalitions. Philip, who grew up as a hostage in one of the civilized city-states, had an eye for what counted there; after returning to Macedon, he made a point of conquering barbarian land that had gold mines, as well as seaports as far as the straits, where the grain trade passed upon which Athens and the other Greek city-states depended. In short, he started by becoming the big frog in a small pond, while learning the military and cultural techniques of his more civilized neighbours, and combining them with the advantages he could see on the periphery.
At a point reached around 340 BC, the city-states woke up to find that their biggest threat was not Persia, nor one of their own civilized powers, but a semi-barbarian upstart, whose armies and resources were now bigger and better than their own.