HELENISTIC GREECE

Classical Greece
Main article: Classical Greece

5th century
Main articles: Greco-Persian Wars and Peloponnesian War
Athens and Sparta would soon have to become allies in the face of the largest external threat ancient Greece would see until the Roman conquest. After suppressing the Ionian Revolt, a rebellion of the Greek cities of Ionia, Darius I of Persia, King of Kings of the the Achaemenid Empire, decided to subjugate Greece. His invasion in 490 BC was ended by the heroic Athenian victory at the Battle of Marathon under Miltiades the Younger. Xerxes I of Persia, son and successor of Darius I, attempted his own invasion 10 years later, but was, despite his overwhelmingly large army, defeated after the famous rearguard action at Thermopylae, and victories for the allied Greeks at the Battles of Salamis and Plataea. The Greco-Persian Wars continued until 449 BC, led by the Athenians and their Delian League, during which time the Macedon, Thrace, the Aegean Islands and Ionia were all liberated from Persian influence.

Delian League ("Athenian Empire"), immediately before the Peloponnesian War in 431 BC.
The now dominant position of the maritime Athenian 'Empire' threatened Sparta and the Peloponnesian League of mainland Greek cities. Inevitably, this led to conflict, resulting in the Peloponnesian War (431-404 BC). Though effectively a stalemate for the vast majority of its length, Athens suffered a number of setbacks during the war. A great plague in 430 BC, followed by the Sicilian Expedition, a disastrous military expedition to Sicily, severely weakened Athens. Sparta was able to ferment rebellion amongst Athens's allies, further reducing the Athenian ability to wage war. The decisive moment came in 405 BC when Sparta cut off the grain supply to Athens from the Hellespont. Forced to attack, the crippled Athenian fleet was decisively defeated by the Spartans under the command of Lysander at Aegospotami. In 404 BC Athens sued for peace, and Sparta dictated a predictably stern settlement: Athens lost her city walls (including the Long Walls), her fleet, and all of her overseas possessions.

4th century
Greece thus entered the 4th century under a Spartan hegemony, but it was clear from the start that this was weak. A demographic crisis meant Sparta was overstrechted, and by 395 BC Athens, Argos, Thebes, and Corinth felt able to challenge Spartan dominace, resulting in the Corinthian War (395-387 BC). Another war of stalemates, it ended with the status quo restored, after the threat of Persian intervention on behalf of the Spartans.
The Spartan hegemony lasted another 16 years, until, when attempting to impose their will on the Thebans, the Spartans suffered a decisive defeat at the Leuctra(371 BC). The brilliant Theban general Epaminondas then led Theban troops into the Peloponnese, whereupon other city-states defected from the Spartan cause. The Thebans were thus able to march in Messenia and free the population. Deprived of land and its serfs, Sparta declined to a second-rank power. The Theban hegemony thus established was short-lived; at the battle of Mantinea in 362 BC, Thebes lost her key leader, Epaminondas, and great loss of manpower, even though they were victorious in battle. In fact such were the losses to all the great city-states at Mantinea that none could establish dominance in the aftermath.
The weakened state of the heartland of Greece coincided with the rising power of Macedon, led by Philip II. In twenty years, Philip had unified his kingdom, expanded it north and west at the expense of Illyrian tribes, and then conquered Thessaly and Thrace. His success was partly due to his innovative reforms to the army. Phillip intervened repeatedly in the affairs of the southern city-states, culiminating in his invasion of 338 BC. Decisively defeating an allied army of Thebes and Athens at the Battle of Chaeronea, he became de facto hegemon of all of Greece. He compelled the majority of the city-states to join the League of Corinth, allying them to him, and preventing them from warring with each other. Philip then entered into war against the Achemaenid Empire, but was assassinated by Pausanias of Orestis early on in the conflict.
Alexander, son and successor of Philip, continued the war. Alexander defeated Darius III of Persia and completely destroyed the Achaemenid Empire, annexing it to Macedon and earning himself the epithet 'the Great'. When Alexander died in 323 BC, Greek power and influence was at its zenith. However, there had been a fundamental shift away from the fierce independence and classical culture of the poleis - and instead towards the developing Hellenistic culture.