The Athenian Empire came to an end when they were defeated by the Spartans in the Peloponnesian War, which lasted from 431-404 B.C. Below is a timeline of that war.
1st Stage of the Peloponnesian War from 431-421
Athens (under Pericles and then Nicias) successful until 424. Athens makes attacks the Peloponnese by sea and Sparta destroys areas in the countryside of Attica. Athens makes a disastrous expedition into Boeotia. They try to recover Amphipolis (422), unsuccessfully. Athens fears more of her allies would desert, so she signs a treaty (Peace of Nicias) that allows her to keep face, basically setting things back to how they were before the war except for Plataea and Thracian towns.
431 - Peloponnesian War begins. Siege of Potidaea.
430 - Plague in Athens.
429 - Pericles dies. Siege of Plataea.
428 - Revolt of Mitylene.
427 - Athenian Expedition to Sicily.
421 - Peace of Nicias.
2nd Stage of the Peloponnesian War from 421-413
Corinth forms coalitions against Athens. Alcibiades stirs up trouble and is exiled. Betrays Athens to Sparta. Both sides seek the alliance of Argos but in the Battle of Mantinea she loses most of her military and becomes an Athenian ally.
415-413 - Athenian expedition to Syracuse. Sicily.
3rd Stage of the Peloponnesian War from 413-404
Under the advice of Alcibiades, Sparta invades Attica. Athens continues to send ships and men to Sicily even though it is disastrous. Athens, which had started the war with the advantage in naval battle, loses this advantage to the Corinthians and Syracusans. Sparta then used Persian gold from Cyrus to build her fleet and destroys the Athenian fleet at the Battle of Aegosotami.
404 - Athens surrenders.
A major contributor to the Athenian defeat was its foolish attack on Sicily. This ill-fated enterprise cost the Athenians an army and a navy at a time they had their hands full battling the Spartans at home. The Athenian plan for Sicily showcased the extreme arrogance of the late empire – an empire that would crumble at the hands of the Spartans.
The Sicilian affair began in the spring of 415 when ambassadors of Athenian Sicilian allies came to Athens asking for help. Two cities in western Sicily, Segesta and Selinus, were in a dispute. Selinus won a battle between them and Segesta appealed to Syracuse for help. Not only was help not given, but Syracuse joined the side of Selinus. The Segestans appealed to Athens for there sense of honor and to protect Sicily against the designs of the Peloponnese (Syracuse was an ally of Corinth who was a member of the Peloponnesean Leagure). They also offered to fund the war.
After much debate in the Athenian Assembly, the decision was made to send a force to Sicily under the command of three generals: Nicias, Alcibiades, and Lamachus. Nicias was reluctant to command the mission, while Alcibiades (nephew of Pericles) was young, charismatic, and all for battle. Lamachus was chosen because he could offer an experienced point of view that would, hopefully, keep the expedition on course.
Things started badly. Just after the army’s departure, Alcibiades was accused of plotting to deface statues of the god Hermes in Athens, and asked to return. Instead he fled to Sparta and joined the Peloponnesean side. Nicias, still reluctant, wasted the first campaign season deciding how to attack Syracuse. He contented himself with building a wall around the city. Then, at the beginning of 414 the Syracusans sent their own envoys to Sparta asking for help. Alcibiades urged the Spartans to defend Syracuse, but they used caution and only sent four ships with no infantry.
Assuming this small fleet was not a threat Nicias worked on his wall, while the Spartans secretly used their allies to increase their force to 3000 infantry and 200 cavalry. They arrived in Syracuse in late 414 and started to construct a wall to counter the wall being built by the Athenians. Lamachus, was killed in a skirmish trying to defend the Athenian wall.
Nicias, now the sole commander and ill with a kidney ailment, realized he would never be able to take the city. He asked to be relieved, but was sent reinforcements under the command of Demosthenes. Not wanting to wait for Nicias to be reinforced, the Spartan commander Gylippus attacked the Athenian fleet in Syracuse harbor and defeated them. Soon after, Demosthenes arrived with plans for an immediate attack, but his two land assaults were unsuccessful during the spring of 413.
By fall, after much argument among the commanders, Nicias decided to withdraw, but was held up by a lunar eclipse on September 13th, which frightened his soldiers. A soothsayer advised that he wait 27 days before withdrawing which gave the Syracusans enough time to attack and destroy the Athenian fleet in the great harbor. Now forced to withdraw by land the Athenians were attacked and defeated. Nicias and Demosthenes were executed. Much of the blame for this debacle rests on Nicias, who was unsure of his goal and overly cautious. He also was carefully guarding his reputation as a winner and unwilling to return home in defeat, fearing the consequences.
This is a classic case of the danger of distance in war (think Viet Nam). The Athenians risked their future on hubris, sending an army far away to a conflict removed from their current struggle. They reinforced a weak commander and wasted an army and navy two times. Thucydides, the great Greek historian, is highly critical of the Athenians for their arrogance during this period. It is hard to get beneath his bias, however, to determine whether the Athenians were as foolish as he makes them out to be. One thing that is beyond dispute – the expedition to Sicily helped produce a Spartan victory in the Peloponnesean War.
The timeline shown came from about.com/ancient history.