The story starts in Macedon, a kingdom to the north of Greece. The Macedonians were warriors and traders. They lived in villages instead of poleis and, while they were recognized as Greeks because of their language and culture, they were also thought of as being a bit like country bumpkins by the more “civilized” Greeks of the south. Macedon was a kingdom ruled by a single monarch, but that monarch had to constantly deal with both his conniving relatives and his disloyal nobles, all of whom frequently conspired to get more power for themselves. Macedon was also bordered by nomadic peoples to the north, particularly the Thracians (from present-day Bulgaria), who repeatedly invaded and had to be repelled. The Macedonian army was comprised of free citizens who demanded payment after every campaign, payment that could only be secured by looting from defeated enemies. In short, Macedon bred some of the toughest and most wily fighters and political operators in Greece out of sheer necessity.
By the fifth century BCE, some of the larger villages of Macedon grew big enough to be considered cities, and elite Macedonians made efforts to civilize their country in the style of the southern Greeks. They competed in the Olympics and patronized the arts and literature. They tended to stay out of the political affairs of the other Greeks, however; they did not invade the Greek peninsula itself in their constant wars, nor did they take sides in conflicts like the Peloponnesian War. This did nothing to improve the situation in Macedon itself, of course, which remained split between the royal family and the nobility. In 399 BCE, Macedon slid into an ongoing civil war, with the nobles openly rejecting the authority of the king and the country sliding into anarchy. The war lasted for forty years.
In 359 BCE, the Macedonian king, Philip II, re-unified the country. Philip was the classic Macedonian leader: shrewd, clever, skilled in battle, and quick to reward loyalty or punish sedition. He started a campaign across Macedonia and the surrounding areas to the north, defeating and usually killing his noble rivals as well as hostile tribes. When men joined with him, he rewarded them with looted wealth, and his army grew.
Philip was a tactical innovator as well. He found a way to secure the loyalty of his nobles by organizing them into elite cavalry units who swore loyalty to him, and he proudly led his troops personally into battle. He also reorganized the infantry into a new kind of phalanx that used longer spears than did traditional hoplites; these new spearmen would hold the enemy in place and then the cavalry would charge them, a tactic that proved effective against both barbarian tribes and traditional Greek phalanxes. Philip was the first Macedonian king to insist on the drilling and training of his infantry, and the combination of his updated phalanx and the cavalry proved unstoppable. Philip attacked neighboring Greek settlements and seized gold mines in the north of Greece, which paid his soldiers and paid to equip them as well. He hired mercenaries to supplement his Macedonian troops, ending up with the largest army Macedon had ever seen.
The Greek poleis were understandably worried about these developments. Under the leadership of Athens, they organized into a defensive league to resist Macedonian aggression. For about ten years, the Macedonians bribed potential Greek allies, threatened those that opposed them, and launched attacks in northern Greece while the larger poleis to the south prepared for war. In 338 BCE, following a full-scale Macedonian invasion, the Macedonian army crushed the coalition armies. The key point of the battle was when Philip's eighteen-year-old son Alexander led the noble cavalry unit in a charge that smashed the Greek forces.
In the aftermath of the invasion, Philip set up a new league of Greek cities under his control and stationed troops throughout Greece. As of 338 BCE, Greece was no longer the collection of independent city-states it had been for over a thousand years; it was now united under an invader from the north. The Greeks deeply resented this occupation. They only grudgingly accepted the Macedonians as fellow Greeks and had celebrated the independence of the Greek poleis as one of the defining characteristics of Greek civilization for centuries. Philip thus had his job cut out for him in managing his new conquest.
The more immediate problem facing Philip in the aftermath of the Greek conquest was that his men demanded more loot – the only way he could pay them was to find new places to invade and sack. Thus, Philip ruled Greece but he could not afford to sit idle with troops aching for more victories. Cleverly, having just defeated the Greek poleis, Philip began behaving like a Greek statesman and assuming a kind of symbolic leadership role for Greek culture itself, not just Greek politics. He began agitating for a Greek invasion of Persia under his leadership to “avenge” the Persian invasion of the prior century. All things considered, this was a far-fetched scheme; Persia was by far the “superpower” of its day, and since the end of the Persian War over a century earlier numerous Greeks had served Persian kings as mercenaries and merchants. Nevertheless, the idea of an invasion created an excuse for Macedonian and Greek imperialism and aggression under cultural pretext of revenge.
Unfortunately for Philip, he was murdered by one of his bodyguards in 336 BCE, just two years after conquering Greece. Family politics was to blame here, as his estranged wife Olympias likely ordered his murder, as well as the murder of his other wife and children. Alexander was the son of Olympias, and he ascended to the throne at the age of twenty.