Corinth attempts to control the strategically important…

The newest Athenian colony is disconcertingly close to another outpost of Corinthian influence at Potidaea in the Chalcidice, and there is a possibility that Athens subjects Potidaea itself to financial pressure by the mid-430s.

An anomaly in being both tributary to Athens and simultaneously subject to direct rule by magistrates sent out annually by Corinth, Potidaea clearly is a sensitive spot in international relations.

Corinth is being indirectly pressured by Athens to the west (Acarnania and other places) and northeast (Amphipolis, Potidaea); …

…this pressure is felt in Corinth's own backyard, at Megara.

Athens passes a series of measures (the “Megarian decrees”) imposing an economic embargo on Megara for violations of sacred land.

The religious aspect of the offense is reflected in the exclusions imposed: like murderers, the Megarians are banned from the Athenian marketplace and the harbors in the Athenian empire.

However, there is no doubt that Athens causes and intends to cause economic hardship as well or that the decrees are the first move in securing Megara as a military asset.

Philip, having enlisted the support of Athens and King Derdas of Elimea, is challenging his older brother Perdiccas for the Macedonian throne by 434 BCE.

Perdiccas responds by stirring up rebellion in a number of Athenian tribute cities, including Potidaea.

Athens responds with force, sending one thousand hoplites and thirty ships to Macedonia where they capture Therma.

They go on to besiege Pydna, where they are met by reinforcements of a further two thousand hoplites and forty ships.

However, as the Athenians are besieging Pydna, they receive news that Corinth has sent a force of sixteen hundred hoplites and four hundred light troops to support Potidaea.

In order to combat this new threat, Athens makes an alliance with Perdiccas, and proceeds to Potidaea.

Perdiccas immediately breaks the treaty and marches to Potidaea, while the Athenians are eventually victorious, the battle (along with the Battle of Sybota) directly leads to the Peloponnesian War.

Anaxagoras, a native of Clazomenae, had brought philosophy and the spirit of scientific inquiry from Ionia to Athens.

His observations of the celestial bodies have led him to form new theories of the universal order.

Anaxagoras describes the cosmos as a continuous field in which different qualities flow and mingle.

He suggests that are not four but possibly thousands of elements and that, as no element can become another, there is no real change but only the illusion of change manifested by the combination, separation and recombination of elements.

He attempts to give a scientific account of eclipses, meteors, rainbows and the sun, which he describes as a mass of blazing metal, larger than the Peloponnese.

The heavenly bodies, he asserts, are masses of stone torn from the earth and ignited by rapid rotation.

However, these theories bring him into collision with the popular faith; Anaxagoras' views on such things as heavenly bodies are considered "dangerous."

This new Ionian science is not well-received by the Athenian public, who view Anaxagoras’ teachings—that the divine mind in this system does not have a human body, and that the Luminaries are not gods but rocks—as deeply irreligious.

Anaxagoras is arrested by Pericles' political opponents on a charge of contravening the established dogmas of religion (some say the charge was one of Medism).

It takes Pericles' power of persuasion to secure his release.

Even so he is forced to retire from Athens to Lampsacus in Ionia in about 434-433 BCE.

Empedocles assumes that there must be more than one kind of matter.

To account for real change, he postulates four roots as elements: earth, air, fire, and water.

Love and hate are considered principles of attraction and repulsion that alternately dominate the universe in a recurring cycle.

A Greek doctor, poet, and philosopher residing in Agrigentum, in Sicily, Empedocles presents a kind of biological theory of natural selection in an imaginative poem, On Nature.

Empedocles also plays an important role in the development of the Western or Sicilian school of Greek medicine.

He articulates the notion that the human body has four humors: blood, bile, black bile, and phlegm, a belief which is to dominate medical thinking for centuries.

He had cured a plague at the Sicilian city of Selinus and claimed he was a god. (One legend, which forms the basis of Matthew Arnold's poem Empedocles on Etna, held that Empedocles, tired of life and wanting people to believe that the gods had taken him with them, committed suicide by leaping into the crater of Mount Etna, but he may actually have died in Greece.)

The humiliated Corinthians have meanwhile constructed a larger fleet while …

…the Corcyrans, with the second largest navy in Greece at this time, appeal to the Athenians, …

…who, taking very seriously the western dimension to its foreign policy (it is about this time that the alliances with Rhegium and Leontini are renewed), vote at first for a purely defensive alliance and after a debate, fully recorded by Thucydides, sent a small peacekeeping force of ten ships to reinforce the Corcyraean fleet, with instructions not to fight the Corinthian fleet unless they attempted to land on the island.

In so doing, Pericles, convinced of the inevitability of war with Sparta and the Peloponnesians, risks the escalation of armed hostilities.

The situation by 433 is serious enough for Athens' finances to be put on a war basis, and, hereafter, the drift to war will continue.