The Corinthian War (395–387 BC) was a conflict in ancient Greece which pitted Sparta against a coalition of city-states comprising Thebes, Athens, Corinth and Argos, backed by the Achaemenid Empire. The war was caused by dissatisfaction with Spartan imperialism in the aftermath of the Peloponnesian War (431–404 BC), both from Athens, the defeated side in that conflict, and from Sparta's former allies, Corinth and Thebes, who had not been properly rewarded. Taking advantage of the fact that the Spartan king Agesilaus II was away campaigning in Asia against the Achaemenid Empire, Thebes, Athens, Corinth and Argos forged an alliance in 395 BC with the goal of ending Spartan hegemony over Greece; the allies' war council was located in Corinth, which gave its name to the war. By the end of the conflict, the allies had failed to end Spartan hegemony over Greece, although Sparta was weakened by the war.

At first, the Spartans achieved several successes in pitched battles (at Nemea and Coroneia), but lost their advantage after their fleet was destroyed at the naval Battle of Cnidus against the Persian fleet, which effectively ended Sparta's attempts to become a naval power. As a result, Athens launched several naval campaigns in the later years of the war, recapturing a number of islands that had been part of the original Delian League during the 5th century BC. Alarmed by these Athenian successes, the Persians stopped backing the allies and began supporting Sparta. This defection forced the allies to seek peace.

The King's Peace, also known as the Peace of Antalcidas, was dictated by the Achaemenid King Artaxerxes II in 387 BC, ending the war. This treaty declared that Persia would control all of Ionia, and that all other Greek cities would be "autonomous", in effect prohibiting them from forming leagues, alliances or coalitions. Sparta was to be the guardian of the peace, with the power to enforce its clauses. The effects of the war, therefore, were to establish Persia's ability to interfere successfully in Greek politics, to atomize and isolate from one another Greek city states, and to affirm Sparta's hegemonic position in the Greek political system. Thebes was the main loser of the war, as the Boeotian League was disbanded and their cities were garrisoned by Sparta. Peace did not last long: war between Sparta and a resentful Thebes resumed in 378 BC, which finally led to the destruction of Spartan hegemony at the Battle of Leuctra in 371 BC.

In the Peloponnesian War, which had ended in 404 BC, Sparta had enjoyed the support of nearly every mainland Greek state and the Achaemenid Empire, and in the months and years following that war, a number of the island states of the Aegean had come under its control. This solid base of support, however, was fragmented in the years following the war. Despite the collaborative nature of the victory, Sparta alone received the plunder taken from the defeated states and the tribute payments from the former Athenian Empire. Sparta's allies were further alienated when, in 402 BC, Sparta attacked and subdued Elis, a member of the Peloponnesian League that had angered the Spartans during the course of the Peloponnesian War. Corinth and Thebes refused to send troops to assist Sparta in its campaign against Elis.

Thebes, Corinth and Athens also refused to participate in a Spartan expedition to Ionia in 398 BC, with the Thebans going so far as to disrupt a sacrifice that the Spartan king Agesilaus attempted to perform in their territory before his departure. Despite the absence of these states, Agesilaus campaigned effectively against the Persians in Lydia, advancing as far inland as Sardis. The satrap Tissaphernes was executed for his failure to contain Agesilaus, and his replacement, Tithraustes, bribed the Spartans to move north, into the satrapy of Pharnabazus, Hellespontine Phrygia. Agesilaus did so, but simultaneously began preparing a sizable navy.

Unable to defeat Agesilaus' army, Pharnabazus decided to force Agesilaus to withdraw by stirring up trouble on the Greek mainland. He dispatched Timocrates of Rhodes, an Asiatic Greek, to distribute ten thousand gold darics in the major cities of the mainland and incite them to act against Sparta. Timocrates visited Athens, Thebes, Corinth, and Argos, and succeeded in persuading powerful factions in each of those states to pursue an anti-Spartan policy. According to Plutarch, Agesilaus, the Spartan king, said upon leaving Asia "I have been driven out by 10,000 Persian archers", a reference to "Archers" (Toxotai) the Greek nickname for the Darics from their obverse design, because that much money had been paid to politicians in Athens and Thebes in order to start a war against Sparta. The Thebans, who had previously demonstrated their antipathy towards Sparta, undertook to bring about a war.

Xenophon claims that, unwilling to challenge Sparta directly, the Thebans instead choose to precipitate a war by encouraging their allies, the Locrians, to collect taxes from territory claimed by both Locris and Phocis. In response, the Phocians invaded Locris, and ransacked Locrian territory. The Locrians appealed to Thebes for assistance, and the Thebans invaded Phocian territory; the Phocians, in turn, appealed to their ally, Sparta, and the Spartans, pleased to have a pretext to discipline the Thebans, ordered general mobilization. A Theban embassy was dispatched to Athens to request support; the Athenians voted to assist Thebes, and a perpetual alliance was concluded between Athens and the Boeotian confederacy.

The Spartan plan called for two armies, one under Lysander and the other under Pausanias, to rendezvous at and attack the Boeotian city of Haliartus. Lysander, arriving before Pausanias, successfully persuaded the city of Orchomenus to revolt from the Boeotian confederacy, and advanced to Haliartus with his troops and a force of Orchomenians. There, he was killed in the Battle of Haliartus after bringing his force too near the walls of the city; the battle ended inconclusively, with the Spartans suffering early losses but then defeating a group of Thebans who pursued the Spartans onto rough terrain where they were at a disadvantage. Pausanias, arriving a day later, took back the bodies of the Spartan dead under a truce, and returned to Sparta. There, he was put on trial for his life for failing to arrive and support Lysander at the designated time. He fled to Tegea before he could be convicted.