By 475 BC Sparta had gained nothing but the hostility of every city or group of cities with which she had tried to interfere. Chief among the anti-Spartan party in Athens was Themistocles and it was his influence that was instrumental in stirring up hostility to Sparta inside the Peloponnese. By 470 Elis the majority of Arcadian cities and Argos, which had almost recovered from the after effects of the battle of Sepeia in 494 BC, were in alliance against Sparta. In 473 BC at the Battle of Tegea Sparta defeats the Tegeans and the Argives and in 471 the Arcadians are defeated by Archidamus II at Dipaea. These two victories re-establish Sparta's position of hegemony in the Peloponnese.
The Delian league was set up ostensibly to
The League consists of:
Athenians, with their naval supremacy, are the de facto leaders and the treasury is established at Delos (hence the name of the league). The hellenotamiai (treasurers) cities contributed money and/or ships. Themistocles had encouraged Athens to build up its fleet between the Persian Invasions, after the war, the Athenians began to fortify the Pireaus and entrances to the harbour were fortified by moles. Later, it would build long walls connecting the two Pireaus and Athens.
Now three classes began to emerge.
Each year the Athenians drew up a list of contributions. All towns had to contribute troops when called upon. Finally, the Athenians gradually asserted the right to hear capital criminal cases in Athens. This generally meant that the well off could be destroyed in the courts if they were felt to be a threat. In 454, the treasury was moved to Athens, the Athenians taking 1/60th for their goddess Athena as a sort of service charge. By now the Athenians had full control of the League, which could now be conceived of as an Athenian empire.
The Delian League gradually became an Athenian Empire. But once the Athenians had it, they found it impossible to relinquish.
The Spartans had been sufficiently concerned with Athenian expansionism to sign a secret pact with the Thasians under which they would invade Attica. The earthquake of 465/464 in which 20,000? Spartans were killed put paid to that and triggered a Messenian and Laconian? helot revolt in 462. Sparta itself was saved by the quick thinking of Archidamos. The Messenians no match for a Spartan field army retreated and established themselves in the natural defences of Mt Ithome in Messenia. In a response to a Spartan appeal to her allies for help Cimon persuaded the Athenians to send aid to Sparta and brings an Athenian force of 4,000 hoplites. The Spartans probably fearing they sympathised with the Messenian cause dismissed them much to the humiliation of Cimon who was exiled on his return. The Spartans eventually take the Messenian stronghold of Ithome.
Athens under the leadership of Pericles begins the breaking of relations with Sparta by forming new alliances with Argos and Thessaly in 459 BC. They also take advantage of a border dispute between Megara and Corinth to detach Megara from the Peloponnesian League and building fortifications that link the port of Nisaia to Megara effectively blocking the route a Peloponnesian army would take on its way to Attica. Also in 459 the Athenians begin to build the 'long walls' connecting Athens to the port of Piraeus. The Athenian alliance with Thessaly improved their military and strategic position. Thessaly was famous for its cavalry and also Thessaly sat on the northern border of Athens' rival Boeotia. The alliance with Argos Sparta's Peloponnesian rival would mean Sparta could not feel secure.
In 457, the first major clash occurred. Nicodemes of Sparta, regent for the under aged king Pleistoanax, bypassed Megara by taking an army of 11,500 hoplites across the Corinthian gulf by sea into Boeotia to help Thebes put down a rebellion by Phocis. Athens took advantage of this to block the routes back to the Peloponnese, and Sparta decided to remain in Boeotia and await the Athenian attack. The Athenians and their allies, under the command of Myronides, had 14,000 men including 1,000 Argives, and met the Spartans at Tanagra. Although the Spartans won the battle after the Thessalian cavalry changed sides, it was a close run thing over two days and they were unable to follow up on their victory; their route home however, was now open. At Oinophyta, led by Myronides the Athenians having regrouped defeated the Boeotians, and then destroyed the walls of Tanagra and ravaged Locria and Phocis. Their victory at Oenophyta allowed Athens to defeat Aegina later in the year, and to finish the construction of the Long Walls to the Athenian port of Piraeus. In 456 Tolmides the Athenian in a demonstration of Athenian naval power took a fleet of 50 ships and burnt the Spartan naval dockyard at Gytheion. He also took the Corinthian city of Chalkis on the Gulf and the small city of Naupactus where they settled the Messenians who had been allowed to leave after the revolt. The treacherous Thessalian were also punished. But the destruction of the Athenian expedition to Egypt, the difficulties controlling their empire and Sparta's reluctance to venture out of the Peloponnese reduced the support for war and in 451 a five year truce was agreed along with a thirty year peace between Sparta and Argos.
In 449 the end of hostilities between Greece and Persia was concluded at the Peace of Callias. A Pan-Hellenic congress is proposed but never meets. The Athenians under Tolmides, with 10,000 hoplites plus other troops from their allies, marched into Boeotia to take back the recaptured towns. They captured Chaeronea, but were attacked and defeated by the Boeotians at Coronea. The Athenians were forced to give up control of Boeotia, and the defeat led to revolts on Euboea and in Megara where the Athenian garrison was killed. In order to get back the many captured Athenians, Athens to secure their safe return abandoned all of Boeotia except Plataea and Thebes resumed its place at the head of a Boeotian league. Pleistoanax' the young Spartan king led an expedition into the Megarid, he turns back at Eleusis , there are accusations of that Pericles had bribed him and his advisor Cleandridas was condemned to death and escaped into exile. Pleistonax was acquitted but also went into exile. The withdrawal of the Spartan army allowed Pericles to suppress the revolt in Euboea.
In 446 a thirty year peace treaty was agreed. Athens agreed to withdraw from Nisaia and Pagae, give up alliances with Phocis, Troezen, Achaea, and to grant self-government to Aegina. An important clause was that both sides would submit to independent arbitration over any disputes over the observance of the terms. When the island of Samos revolted in 440 BC against Athens, Sparta tried to get the Peloponnesian League to declare for war but they could not persuade the majority of members to vote with them. Here we see one of the fundamental differences between the so-called Athenian democracy's Delian League and the 'oligarchic' Spartan league, in the Peloponnesian League each member however small or great had just one vote whereas as has been shown any disagreement by a Delian member against Athens' will resulted in military action against them.
Thucydides an Athenian general, exiled during the course of Peloponnesian war began his history when war broke out; lived through war, but his account remained unfinished, the reasons for the war, according to Thucydides were that the underlying cause had to do with Spartan fear of the growth of Athenian power. The immediate pretexts were the dispute between Corcyra and Corinth, Epidamnus, and the defensive alliance between Corcyra and Athens. The naval Battle of Sybota took place in 433 BC between Corcyra and Corinth. Both the Corinthians and Corcyraeans claimed victory, the Corinthians having won the first battle, and the Corcyraeans having avoided a Corinthian occupation of their island. In 432 the Corinthians and Athenians clashed again. Potidaea was a colony of Corinth on the Chalcidice peninsula, but was a member of the Delian League and paid tribute to Athens. After Sybota, Athens demanded that Potidaea pull down part of its walls, expel the Corinthian ambassadors, and send hostages to Athens. Athens was afraid that Potidaea would revolt due to Corinthian or Macedonian influence, as Perdiccas II of Macedon was encouraging revolts among Athens' other allies in Thrace. The Athenians succeeded in defeating a Corinthian force and cut off Potidaea from the sea with a naval blockade. In early 432 B.C. the Athenian assembly passed the Megarian Decree, which excluded Megarian merchants from the markets of the Athenian Empire. The Assembly of the Peloponnesian League held at Sparta in 432 put the Spartans under considerable pressure to restrain the Athenians. On the one hand Archidamus argued that Athens was fitter to conduct a long war and negotiations had not been exhausted. On the other hand the ephor Sthenilaidas demands decisive action. Corinth persuaded the majority of the League that Athens had broken the terms of the peace but even now Sparta was reluctant and embassies were sent to Athens to negotiate a settlement. Pericles convinced the Athenian assembly to reject the offer and the inevitable came to pass.