Originally Posted by
pannonian
The Spartans were almost invincible in the field, but they weren't very good at storming fortifications, so each year would see the Spartan army march out during the campaigning season, burn as much of the Athenian fields as they could (since they couldn't take the city), before returning before their slaves revolted in their absence. However, Athens had absolute command of the sea, having more ships and better sailors, and they could feed themselves with grain imported from the Crimea. With Athens unable to contest on land, and Sparta unable to contest at sea, the war became a stalemate.
This changed with a Spartan politician-general called Lysander. He used his friendship with the Persian prince Kyros to gain Persian money, with which he built ships and bought other Greek sailors, pricing Athens out of the market. He was also a decent admiral in his own right, and he slowly reduced the Athenian fleet and their ability to collect tribute or transport grain to Athens. After the destruction of their final fleet, Athens was left with no sea supply at all, and Sparta followed up by besieging Athens from land. After a year of starvation and disease, the Athenians surrendered, bringing the Peloponnesian War to an end. Athens' walls were pulled down, the Athenians weren't allowed a navy, democracy was abolished and a pro-Sparta oligarchy put in place, and the leaders of the resistance against Sparta were executed.
The Spartan domination didn't last, as Athenian democrats secretly helped the Thebans restore their independence, led by Pelopidas and Epaminondas. The Thebans pioneered a new way of warfare, that emphasised innovation and flexibility, and repeatedly thrashed the Spartans who stuck to their old battering ram tactics.
One of those most struck by this new Theban age was a Macedonian hostage called Philip, who was inspired by his time in Thebes to reform the Macedonian army. This radically new Macedonian army would later be used by Philip to unite all of Greece, and later used by his son Alexander to conquer the Persian empire.