Alexander III was twenty years old at the time of his father's death in 336 BC. Although Philip had offspring from several of his wives, Alexander was treated as his father's heir throughout Philip's reign and groomed for his future role. Greek tutors provided him with an education in Greek literature and culture. Alexander also had practical training in kingship. But his succession was not assured. Olympias and his closest friends and advisers were in exile, and there were rumors implicating him in Philip's assassination. Antipater, Philip's most senior commander, saved the succession for Alexander by presenting him to the troops for the acclamation as king.
Philip's senior commanders urged Alexander to consolidate his base in Macedon. He went to Greece instead, forcing politicians at Athens and Thebes to abandon plans to free Greece. Alexander was confirmed in Philip's positions as archon of Thessaly and hēgēmon of the Corinthian League, and Greek support for the war against Persia was reaffirmed. Then he campaigned as far north as the Danube and subdued Thracian tribes. When the Thebans revolted, he sold them into slavery after destroying the city. In Macedon, Alexander quickly eliminated all potential rivals.
Alexander invaded Asia in 334 BC with an army of 37,000 and a fleet of almost two hundred Greek ships. He needed a quick victory. He had sufficient funds for only a brief campaign. Moreover, his friends did not control the government and the army. And he had left almost half his Macedonian troops behind to control Greece and Macedon
Satraps normally employed a defensive strategy that would deny the enemy use of local resources until the Great King could mobilize the empire's main forces. The Anatolian satraps decided to confront Alexander directly in battle and almost succeeded in killing him at the River Granicus. They failed, and their army was totally destroyed. In quick succession the satrapies of Lydia, Caria, and Lycia fell to Alexander. By 333 BC, he had reached Gordium, severing Anatolia from the Persian Empire.
After his victory at the Granicus, Alexander ordered Greek and non-Greek cities that surrendered to obey their new Macedonian satrap and to pay the same tribute they had paid to the Persians. He encouraged democratic factions in the Greek cities of Asia when they offered their support to the Macedonian forces. But the newly "liberated" cities now had to make financial contributions to the Macedonians and were punished if they objected. Non-Greek leaders who recognized Alexander could expect royal favor.
A fever delayed Alexander's departure from Anatolia until 333 BC. Then, instead of seeking to confront the forces of Darius III in Mesopotamia, he moved south along the coast toward Egypt. He hoped to end Persian naval operations in the Aegean by depriving the Persian fleet of its bases. At the same time, Darius III led the Persian Empire's forces northwestward from Babylon, hoping to trap Alexander in Anatolia. At Issus in Cilicia, Alexander confronted the Persian army. Despite the Persians' numerical superiority, they were defeated by the Macedonians. Darius was forced to abandon his army and flee. The royal treasure stored at Damascus fell into Alexander's hands. Alexander also captured Darius' family, including his mother, wife, and son. He rejected Darius' offer of friendship and alliance in exchange for his family's return.
Alexander resumed his march toward Egypt. Most of the Syrian and Phoenician coastal cities surrendered. Only Tyre and Gaza resisted but they fell to Alexander, who slaughtered the male population and sold the women and children into slavery.
In Egypt, the last Persian satrap surrendered without a fight. The Egyptians had never accepted Persian rule and welcomed Alexander's army during its march to Memphis. At Siwah he consulted the oracle of Zeus-Ammon. The chief priest of the oracle greeted him as "Son of Ammon." The Greeks understood that the priest had recognized Alexander as a son of Zeus. In 331 BC, Alexander founded Alexandria. It was a Greek polis with citizenship limited to Greeks and Macedonians. He appointed a single satrap for Egypt and retained much of its Persian organization.
Alexander sought a final confrontation with Darius III, who tried to avoid battle by making a proposal. Alexander refused, and the two armies met in 331 BC, at Gaugamela. Alexander won and Darius fled. The heartland of the Persian Empire was now Alexander's for the taking and his troops saluted him as king of Asia.
Alexander captured Babylon and Susa and rewarded the satraps who had surrendered them by leaving them in their positions. Next came Persepolis, the spiritual center of the Empire. In revenge for the destruction wrought during the Persian wars of the early fifth century BC, the Macedonians torched the city's palaces after stripping them of their treasures.
Eastern satraps, headed by Bessus, assassinated Darius III in 330 BC. Bessus escaped to Bactria, where he assumed the throne of Persia as Artaxerxes IV. Alexander no longer acted as the avenger of past Persian misdeeds. He now assumed the role of Darius' successor and defender of Achaemenid legitimacy against the regicides. Persian nobles and some surviving members of the Achaemenid house joined Alexander, and Bessus was betrayed to Alexander, tried, and executed as a regicide.
Alexander's ignorance of conditions in the east ignited rebellion throughout Sogdiana and Bactria. In 327 BC, after a three-year revolt, Alexander replaced Iranian satraps with Greek and Macedonian officials. He also settled Greek mercenaries and discharged veterans in military colonies.
Alexander's soldiers became more reluctant to advance farther into Asia. They longed for home and worried about his abandonment of the traditional Macedonian style of kingship. In 327 BC Alexander married Roxane, the daughter of a Sogdian noble.
Conspiracies against Alexander's life began in 330 BC. Philotas, the commander of the companion cavalry, was executed for failing to inform Alexander of an alleged plot to kill him. In 328 BC, Alexander murdered Cleitus for criticizing Alexander's efforts to accommodate the Persians and his belittling the contribution of his soldiers to his successes. Alexander was nearly assassinated six months later by some of his pages.
When Alexander entered India in 327 BC, he found a vast subcontinent occupied by a network of peoples and states. As the Macedonian army descended through the Khyber Pass to the plain of the Indus River in 327 BC, it encountered fierce resistance. Opposition ended at Taxila, whose ruler had earlier solicited Alexander's aid against his eastern neighbors Abisares and Porus. In 326 BC, the armies of Alexander and Porus met at the Hydaspes River. Alexander totally destroyed his enemy's forces.
As the army marched farther eastward, morale dropped steadily, and at the river Hyphasis the soldiers mutinied. Alexander yielded and agreed to return to the Indus.
Ancient and modern historians have speculated about Alexander's ultimate goals. Whatever they may have been, his army forced him to adopt a modest goal: the conquest of the Indus River Valley to its mouth. As his army moved steadily southward there was heavy resistance and unparallelled slaughter. In July 325 BC, the army reached the mouth of the Indus, and preparations for the journey home began.
Alexander's achievements in India were ephemeral. Although he had planned carefully for his Indian domain, the resources available to his agents proved inadequate to maintain Macedonian rule there.
Alexander left India for Persia in late August 325 BC. He intended to lead eighty thousand people, including soldiers, their families, and camp followers, through Gedrosia. Before the army reached Carmania and safety, thousands died, swept away in a flash flood.
When Alexander returned from India, eight satraps and generals were deposed and executed. Most were guilty of assuming that Alexander would not survive and had begun to exploit his empire for their own personal benefit. To prevent similar problems in the future, all satraps were ordered to disband their mercenary forces.
In the early spring of 324 BC, Alexander celebrated the conquest of India. The climax of the celebration was a marriage ceremony in which Alexander took as wives daughters of Artaxerxes III and Darius III. In the same ceremony ninety of Alexander's officers married noble Persian and Median wives. Then Alexander introduced into the army thirty thousand young Iranian troops trained to fight in Macedonian style, whom he referred to as his "Successors." When he announced in 324 BC that he intended to discharge and send home veterans who were too old or too ill to fight, the army mutinied. Only after Alexander reassured them that his Macedonians were his only true "companions" did the mutiny subside; but shortly thereafter he discharged the veterans and sent them back to Macedon.
On his arrival at Babylon in 323 BC, omens of his impending death were already being bruited about. On May 29, Alexander fell ill at a party, and he died on June 10, 323 BC. According to later legends, he was the victim of a plot. More likely, his body, exhausted by the strain of constant campaigning and numerous wounds, was unable to fight off a disease, possibly malaria.