Other districts under federal systems join Boeotia: Euboea, Acarnania, Phocis, Thessaly, Arcadia, and Achaea.

However, this great block of military power is soon split by imperialist ambitions, and the Boeotian League itself intervenes in the Achaean League in 366, when Epaminondas invades the Peloponnese for a third time, with a view to strengthening the Theban position there.

He obtains assurances of fidelity from several states and, perhaps because of these assurances, decides not to overthrow the oligarchical governments that the Spartans have established.

This is unacceptable to the Theban government, which is in favor of overthrowing the oligarchs and establishing new democracies.

Thebes, when the city's proposals at Susa inevitably fail, seizes the valuable border territory of Oropus, and …

…Athens is after all obliged to accept what is probably a King's Peace (366).

There is, however, no question of Athens dismantling its navy; on the contrary, its claims to the Chersonese (reachable only by sea) are recognized in exchange, it seems, for acceptance of Theban leadership of Boeotia, including Oropus.

Athens' pursuit of essentially private Athenian aims, such as control of Amphipolis and the Chersonese, cannot have pleased its allies in the confederacy.

It is costly, and it is ultimately unsuccessful.

On the other hand, Athens, shortly after the peace of 366, does send help-—a force under Timotheus—to a rebel satrap, Ariobarzanes of Hellespontine Phrygia; this shows a perhaps encouraging willingness to defend Greek interests against Persia, especially since …

…Timotheus ejects a Persian garrison he finds installed on Samos, a violation of Persia's side of the original King's Peace.

It is surprising that Athens should act against Persia so soon if the peace of 366 is really a King's Peace, but the risk of reprisals at this time is slight.

In any case, Timotheus' somewhat contradictory instructions are to keep to the King's Peace while also helping Ariobarzanes.

Dion, a former minister and a relative of the older Dionysius by marriage, had invited Plato back to Sicily in order to undertake the philosophical and scientific education of the young Dionysius and generally to educate him to become a constitutional king.

Plato had accepted.

Perhaps he intended to foster the establishment of a philosopher-king, as set forth in his "Republic."

However, Plato's experiment ends in failure the following year with the dismissal of both counselors; Dion goes into exile and Plato returns to Athens.

Dionysius, weak and ineffectual, lacks the vigor to maintain the military autocracy he has inherited, ruling precariously in Syracuse and southern Italy.

Timotheus, upon his acquittal of a charge of negligence in 373 BCE, had served the king of Persia as a mercenary, and is now back in the service of Athens.

He overruns Samos after a ten-month siege in 366-365 BCE, and installs an Athenian cleruchy on Samos, a capital error.

Timotheus' action can be technically justified: Samos is not a member of the Athenian Confederacy, and Persia had violated the King's Peace by installing its garrison; thus the cleruchy can be seen as a military response to Persian provocation in an area not covered by the rules of the charter of 377 BCE.

Its effect on Greek opinion is damaging nonetheless, and …

…the Thebans quickly try to exploit it.

Timotheus goes on to capture a number of cities in the northern Aegean, but fails in two seaborne attempts to take Amphipolis.

Dionysius II of Syracuse sends help to Sparta, enabling it to recover control over some formerly subject communities in 365, but that is about the limit of his interference in mainland Greek affairs.

Perdiccas kills Ptolemy in 365 BCE and assumes control of Macedon’s government.

Of the reign of Perdiccas we have very little information, knowing only that he was at one time engaged in hostilities with Athens on account of Amphipolis, and that he was distinguished for his patronage of men of letters.

Among these, we are told that Euphraeus, a disciple of Plato, rose to so high a place in his favor as completely to govern the young king, and exclude from his society all but philosophers and geometers.

He also served as Theorodokos (sacred envoy-receivers, whose duty is to host and assist the Theoroi, or "viewers" before Panhellenic Games and Festivals) in the Epidaurian Panhellenic games of about 365 BCE.