Following the end of the Corinthian War under the peace treaty in 387 BCE, Sparta would go on to seek revenge against the states that had combined against it during the war, as well as to ensure that no such events could occur again. To this end, it used the terms of the peace of stop the formation of all alliances that it could under the pretense of preserving the autonomy of the city-states as guaranteed in the peace imposed by Artaxerxes. Though beneficial in the moment for maintaining dominance over Greece, these actions would serve to further enrage the Greek city-states that opposed Sparta.
In time, this general feeling of ill-will against Sparta would lead to yet another war with the objective of breaking Spartan military hegemony over Greece. In 378 BCE, a revolution against the pro-Spartan government that had been instituted in Thebes would begin the event known as the Boeotian War (though it would not be wholly inappropriate to call the Boeotian War an extension and late continuation of the Corinthian War, as the political dynamic of Greece under Spartan rule was the cause for both events). This revolution had been supported by two generals from Athens, which was still in a weaker position that Sparta, though it had recovered much of the power that it had lost in the Peloponnesian War between the two. In an attempt to quell the rebellion as quickly as possible and to prevent another war between itself and the many Greek city-states that it had dominated under the Persian peace treaty, Sparta immediately declared war and sent a force under the new Agiad king Cleombrotus I to attack the new Theban government and the supporting Athenian forces in Boeotia. Cleombrotus failed in his efforts to retake Thebes, but did succeed in forcing the withdrawal of the Athenian forces.
The war might have ended at the point of the Athenian withdrawal had it not been for the unsanctioned actions of a Spartan general by the name of Sphodrias, who had been left in command of a small force in Boeotia. Sphodrias, without orders to do so, launched an assault against the port city of Peiraeus in Attica, which at that time was one of the main ports used by Athens. However, the attack was never completed, as the night march of the Spartan force took longer than Sphodrias had intended, forcing him to retreat when the sun revealed the approach of his column. The ill-planned attempt at attacking an Athenian-allied city brought Athens into the war in full force, and the Boeotian War was begun.
The failures of Cleombrotus in his earlier campaign against Thebes led to his removal as the commander of the war, with the vastly more experienced Agesilaus II, still the king of the Eurypontid line, replacing him in command. Agesilaus had a record of pursuing harsh policies against Thebes for its efforts against Sparta in the past, and had been held back from the initial campaign out of concern that an attack led by him might have resulted in more Theban resentment against Sparta. Now that a larger war was building, however, the Spartans decided that the armies in Thebes were best left in his command. In 377 and again in 376, Agesilaus would lead campaigns into Boeotia to raid the lands and destroy the resources vital to Thebes. Despite his success in this effort, he failed to achieve a decisive victory that would put a stop to the war.
At the same time, Athens was making ready to escalate the war still further via the formation of a new anti-Spartan alliance, something which had until this point been strictly forbidden by Sparta as a violation of the terms of the peace treaty that had been imposed by Artaxerxes II at the end of the Corinthian War. Now that the peace treaty had already fallen apart, however, there was nothing to stop the Athenians from once again creating a league of city-states that would combine to break Sparta's hegemony over Greece. At the same time, the Peloponnesian League was revived as a practical political institution, and troops began pouring in from Sparta's allies to support it in its military efforts against Athens and Thebes. By 375 BCE, the political division of Greece into Spartan and Athenian camps that had briefly been halted (at least as a formal matter) at the end of the Corinthian War was once again in full force.
As had been commonplace in other wars with Sparta, an Athenian fleet was sent to raid the coast of the Peloponnese, pressuring Sparta and its allies. At the same time, the Thebans, now the great rising power of Greece, began a series of conquests in Boeotia, targeting both Spartan allies and city-states that traditionally allied themselves with Athens, leading to tension between the two main members of the anti-Spartan alliance that had been formed for the war. In either 375 or 374 BCE, the peace between Athens and Sparta was reinstated with the support of Artaxerxes, who was planning an invasion of Egypt for which he would require Greek mercenaries. The peace would not last, as an Athenian admiral returning from the raids on the Peloponnese would assist the anti-Spartan democratic government of Zacynthus, which had recently been exiled in favor of a pro-Spartan regime. This action brought the two city-states into a proxy war with each other once more. The reinstatement of peace, however, would likely have done little to stop the war as a practical matter, as Thebes was not among the parties that had agreed to it, meaning that the peace would only have reduced Spartan opposition from Athens while the Boeotian states under Thebes would have continued to resist Sparta as they did anyway.
The general state of low-level war would continue until 371 BCE, when a lasting peace agreement would finally be put into effect, again with the support of Artaxerxes. This time, the Thebans were brought in as parties to the peace agreement, and the end of the war must have seemed certain to those who were engaged in the negotiations. The terms of the new treaty would return full autonomy to the city-states that signed, and would allow for cities to form alliances with each other if any city came under attack in violation of the terms. Thebes, at last, agreed to the peace, but after already having made the pact demanded that they be allowed to sign in place of all of the Boeotian city-states, much as Sparta had done for the states of the Peloponnesian League. Both Athens and Sparta denied the request, likely at the behest of the anti-Theban Agesilaus. Thebes, refusing to allow for the autonomy of the states in Boeotia, found itself the lone force in opposition to Sparta, which would now be forced to make war on it more directly. The ensuing battles with Thebes would be the beginning of a long decline for the once great martial city-state of the Peloponnese.
Due to an illness, Agesilaus had previously relinquished his command of the Boeotian armies back to Cleombrotus, who had stationed the Spartan forces now under his command in Phocis by the time of the peace negotiations and their eventual breakdown. A great debate was held among the assembly of Spartan citizens, which eventually ruled in favor of authorizing the king to once again attack Thebes and its Boeotian allies. The resulting battle would take place at Leuctra, where the Thebans and Spartans would attack each other out of a mutual political necessity to maintain the image of strength among their allies. Knowing the Spartan tradition of placing the king and his royal guard of the 300 soldiers of the hippeis on the far extreme of the right flank of the Spartan line, the Thebans under the command of a general named Epaminondas massed their best infantry forces against the Spartan right in order to break the line at its strongest point following an onslaught of cavalry to weaken it. When the line broke under this attack, the most elite faction of the Spartan military was massacred, including Cleombrotus himself. In disarray and shocked at the defeat of the best soldiers that Sparta could field, the remaining Spartan force and their Peloponnesian allies withdrew in defeat.
From the historical perspective, the Battle of Leuctra is commonly seen as the turning point for Sparta. Once the greatest military force in Greece and virtually unbeatable in the minds of many of its opponents, the Spartans had lost their aura of invincibility and, more importantly, the prestige that had had come with their exploits in battle. In the aftermath of the battle, Athens offered no support to Thebes, but relished the opportunity to exploit the newly weakened state of Sparta to prevent it from being the sole enforcer of the peace treaty set out by Artaxerxes. Much worse for Sparta, the Thebans were not satisfied with securing Boeotia, but now sought to punish Sparta for its actions against their expansion.
In 370 Thebes, having gained an informal state of military hegemony over Greece with the defeat of Sparta at Leuctra the previous year, undertook an unprecedented series of land campaigns to invade the Peloponnese and, eventually, even Laconia itself, the first time since the Dorian migration into Laconia that an enemy land force had ever moved directly against Spartan territory. This in and of itself is evidence of the psychological effects that Leuctra had in the Greek world. Before the defeat of the Spartan force there, a land campaign against the Spartan infantry on its own ground would have been completely unthinkable. This series of campaigns would be separated into four invasions of the peninsula in 370, 369, 367 and 362 BCE and would be led by Epaminondas, who had proven the effectiveness of his new tactics against the Spartans in the field. .
The campaign of 370 BCE resulted in the crossing of Theban armies into Laconia through the Eurotas valley. The Spartans, however, decided on a defensive action, securing their position at Sparta itself and allowing the Thebans to raid the countryside and surrounding cities. Though Sparta itself was not challenged, the fact that the armies of Thebes were able to do great damage to Laconia was a clear signal that the balance of military power had shifted from Sparta to Thebes. In the same campaigning season, Theban forces moved against Messenia, which the Spartans had held complete dominion over for well over two centuries. Freeing the Messenian Helots and breaking the Spartan grip over the land, the Thebans simultaneously deprived their Laconian adversaries of a massive amount of labor force and productive land, as well as stripping away from Sparta one of the areas over which its control was thought to be absolute.
The advances made in the invasion of 370 followed by a less successful campaign in 369. Sparta, now allied with Athens out of mutual concern about the militaristic expansion of power by Thebes, fought a defensive action on the Isthmus of Corinth, only to once again have its lines broken by Epaminondas, who by now had no fear of Spartan infantry. Once inside the Peloponnesian lands, however, the invading Thebans did little but raid countryside, failing to take any major cities, despite help from Argos. Another invasion followed two years later in 367 BCE, when Theban and Argive forces combined to overthrow many of the pro-Spartan oligarchies that had been established on the peninsula during Sparta's long period of hegemonic dominance. While this effort was successful, the results would be short-lived. As soon as the Theban forces had withdrawn, the ousted governments, with the military backing of Sparta, removed the new democratic governments that had been forcibly established by the armies of Thebes.
The final invasion of the Peloponnese led by Epaminondas would come half a decade later, in 362 BCE. The Theban commander had now shown himself so successful against the Spartans in the field that Thebes had come to hold a degree of military prestige over even Sparta and Athens. This campaign would culminate in the Battle of Mantinea, named for the city-state near which it was fought. Mantinea, one of the few remaining allies of Sparta, had held out against the imposition of Theban dominance, and had requested military assistance from Sparta in order to maintain autonomy. Sparta, likely sensing a need to show strength in the face of the rising Theban forces, agreed to send its armies, along with those that could be gathered from other allied states opposed to Thebes, to Mantinea to render whatever assistance they could. The resulting battle, however, would help neither side with its result.
The Spartans, led by Agesilaus II, were determined to finally score a decisive victory against the Theban general who had defeated them at Leuctra and mounted multiple incursions into their sphere of influence in the nine years that had followed. However, Epaminondas once again proved the superiority of his battlefield tactics, defeating the combined forces of the Spartan alliance by launching a light and fast cavalry assault against the Spartan mobile cavalry before pouring everything he could muster against the Spartan line, particularly where the weaker and less-experienced Mantinean forces were positioned.
Though the Thebans would once again defeat the Spartans in the field, the victory would come at a massive cost that would ultimately stop the military ambitions of Thebes in their tracks. Before the battle ended, Epaminondas was killed by a Spartan soldier whose name is disputed among various histories, but who undoubtedly changed the history of Greece by his action. In the fighting, the two next-highest Theban commanders were also killed, depriving Thebes of the military leadership that had managed to show up the once unbeatable Spartan infantry time and again. With this loss, the Theban army, which had incurred heavy casualties but ultimately won the Battle of Mantinea, would no longer be able to assert its military power in the Peloponnese. Sparta, however, had fared little better. Its defeat in yet another major infantry engagement would forever lay to rest any hopes of it returning to the power and glory that it had enjoyed earlier in the Classical Period when it was, by far, the dominant land power in the Greek world.
It must, however, be recognized that Sparta did not suddenly fall apart and end its history with the Battle of Mantinea and the aftereffects thereof. It would continue to exist, but would never again be the preeminent military power of Greece. Agesilaus, the last Spartan king who had played a hand in the military hegemony of his city-state, would eventually die in Libya and be succeeded by his own son, Archidamus III. Archidamus himself would continue on his father's military legacy, leading Sparta in the Third Sacred War, the conflict that would bring Greece under the hegemonic control of Phillip II, then king of Macedon and more notably the father of Alexander the Great, whose multi-national empire would soon supplant the traditional power structure of both ancient Greece and the Persian empire itself.
Sparta, however, would remain a power so great in its own territory that even Phillip could not take it. It would sit out the combination of every other Greek city-state with the growing Macedonian empire, and would even ally with the Persians to make war against Alexander the Great under the rule of king Agis III. This campaign, however, would end in disaster, as Agis would be killed in combat and the Spartans forced to make peace with Macedon against their will.
From this point forward, the arc of Spartan history follows a long and slow path to an inglorious end far from the city-state of militaristic legend that it had been at its height when it had battled Persia and Athens. Even the ancient Lycurgan laws, the very backbone of Spartan society, began to break down. By the 3rd century BCE, the laws concerning the equal distribution of wealth and property had broken down, creating a situation not entirely dissimilar to what Lycurgus had attempted to correct through his laws so many centuries before, if the historical accounts of his life are to be believed. Thus, it would appear, had Sparta come full circle.
For a brief period toward the end of the 3rd century, a moderate return to Spartan dominance seemed as if it might occur. The shift occurred under a series of reforms instituted by one of the last kings of the Agiad line, Cleomenes III. In an attempt to return Sparta to the Lycurgan system that had made it the greatest power of ancient Greece, Cleomenes implemented a series of economic reforms intended to once again distribute wealth equally amongst the full citizens of Sparta. He also attempted to revive Sparta's military tradition, which had not yet fully declined into obscurity, by instigating a war with the Achaean League, an alliance that had existed first in the 5th century BCE and had been revived by Achaea following the end of Spartan dominance and the beginning of Macedonian hegemony. Though these measures would have at least some effect on Spartan society, they would be insufficient to restore it to its former glory. The wealthy among the Spartan populace rejected the reforms regarding land distribution, and Cleomenes' attempts to make war on Sparta's neighbors would be stifled by the Ephors who were against exercising military might in the field at that time.
In 222 BCE, the Spartan conflict with the Achaean League would reach its climax at the Battle of Sellasia, in Laconia itself. The Achaean League, now allied to the Macedon, would defeat the bulk of the Spartan land forces, cementing its victory over Sparta. The battle would also result in the exile of Cleomenes, largely demolishing what must have briefly looked like a promising chance for Sparta to reassert itself. The defeat was so great that even one of the most ancient of Spartan institutions, that of the dual kingship of the Agiad and Eurypontid lines, would fall apart for a short time. Between 221 and 219 BCE, Sparta adopted a more republican form of monarchy. The experiment would fail and the dual kings would return, but only briefly. The final ruling king, ironically, would himself be named Lycurgus, the 30th king of the Eurypontid house. Technically, his son Pelops would be the last king of Sparta. However, Pelops was assassinated in or around 206 BCE as a child, meaning that he never ruled in his own right. With his death, the monarchies of Sparta (the Agiad line already having come to an end during the time of Pelops' father) completely ceased to exist.
Next would come a brief period of Sparta under a series of three tyrants, though these tyrants would claim descent from the kings of old. The most prominent of these, Nabis, would rule from 206 until 192 BCE. Accounts of his reign are likely exaggerated, as they tend to portray him as little more than a thuggish criminal ruling by brutality. A more balanced view of his rule leads to speculation that he may have been making yet another attempt at reform. Whatever the case may have been, it was under Nabis that an ancient power in severe decline came into conflict with the new power of the region which was very much in its own ascent. In 195 BCE, Sparta was attacked by Rome. It had once again managed to seize control of Argos, its ancient enemy, from the Achaean League, which appealed to Rome for assistance. The war would take place in Laconia and result in a Spartan defeat, though not a decisive one. Three years later, in 192 BCE, Sparta was finally incorporated into the rising power of the Achaean League. Within half a century, the league and by extension Sparta itself would come under Roman rule.
The city-state of Sparta itself would survive well into the common era, not being completely abandoned until the end of the Roman era. Indeed, throughout the military history of Rome, Spartan troops would, from time to time, find their place on the battlefield in the service of the new empire, and the city would eventually become perhaps the world's first living history museum, in which Roman tourists could see Spartan life as it had evolved in Greece's Archaic Period continue on in the highly traditional society. The great events of Spartan history, such as the conquest of Messenia and much of the rest of the Peloponnese, the last stand of Leonidas and his royal hippeis against the vastly superior Persian force at Thermopylae and the extension of Spartan power over all of Greece in the Peloponnesian War were, however, now things of the distant past. Sparta's moment of prominence in history had passed.
Regardless of the end to which it came, the historical legacy of Sparta should not be underestimated. It was, without question, one of the two greatest city-states of ancient Greece (the other being Athens), and indeed generally found itself in a position greater than its competitor. In aiding the effort to keep Greece free of Persian rule, Sparta had facilitated the Golden Age and the advances that came with it, though it did not partake of nor participate in many of them itself. Its military prowess, too, would go on to become nearly the stuff of legend. Indeed, the Spartan tendency to forgo pleasure in favor of utilitarian functionality and the achievement of the ultimate ends of the society would even give this ancient Greek city-state a place in the English language in the form of the more or less common word “Spartan.”