Perdiccas helps the Spartan Brasidas in 424 BCE to take Amphipolis from the Athenians, one of her most important colonies, mainly for its ready access to timber for her fleets.

This is a severe blow to Athens, and will tie them to Macedonian timber for years to come, which strengthens Macedonia’s bargaining power considerably.

In return for this, the Spartans help Perdiccas secure his borders, by leading an assault on King Arrhabaeus of Lyncestis, with the promise of support from the Illyrians.

However, the Illyrians switch sides and attack Perdiccas and his Spartan allies.

The poorly trained Macedonian troops flee, and so the Spartans also retreat and attack the Macedonian baggage train in anger.

This sours relations between Macedonia and the Peloponnese for years to come, and pushes Perdiccas closer to Athens, with whom he will ally Macedon in 423.

The consequent decline in morale prompts Athenian general Nicias, a leader of the aristocratic party who has fought loyally against Sparta although opposing the expansionist policies of the democratic party, to lead an Athenian peace party in opposition to Cleon.

This causes Athenian war policy to be decided politically with increasingly disastrous results.

Aristophanes, in The Knights (424), mounts a savage attack on the imperialist Cleon, caricaturing the popular Athenian demagogue as a slave of Demos (Sovereign People).

Athens makes a serious and initially successful attempt, under Demosthenes, on Megara and its port, Nisaea, followed by …

…a failed campaign at Delium in Boeotia, where a Boeotian hoplite army with a deepened right wing, whose key component is Theban, defeats Athens. (Alcibiades pays his debt to Socrates when he protects his friend in the flight from the battle.)

The balance of the war begins at this point to tilt again in Sparta's favor.

Athenian allies Olynthus and other cities, their taxes trebled by Cleon to help pay for the war, revolt in 424 and seek Spartan support.

The Spartans send General Brasidas, who had first distinguished himself in combat in 431, to invade Thrace with less than two thousand helot hoplites and mercenaries.

The Spartans advance through Thessaly, defeat two Athenian forces en route, and frustrate the Athenian attack on Megara.

Brasidas immediately sets about breaking up the Athenian empire in the north, using a blend of cajolement and threats to win over to Sparta the cities of Acanthus and …

…Stagirus (both in Chalcidice) and …

…most important, the Athenian colony of Amphipolis, canceling the advantage gained by the Athenians at Sphacteria.

Thucydides (the historian), in command of a naval squadron, had arrived too late to supply the reinforcements urgently requested by the Amphipolitan soldiers, but …

…his troops manage to prevent Brasidas' small force from capturing the nearby port of Eion.

Brasidas, however, proceeds to capture Torone. (Thucydides will subsequently, be banished from Athens for twenty years for his failure to protect Amphipolis from the Spartans.)