A violent antipathy to Sparta in the Greek world at large was created after the Spartans had destroyed the power of Athens in 404. Sparta, under the command of Lysander, had established oligarchies and installed garrisons in several cities. They even raised taxes to afford combined taxes, so they claimed. This way they repeated the huge mistakes Athens had made with her Delian League in the previous century. The only difference had been that Athens had installed democratic puppet governments while Sparta had installed oligarchic ones.
Sparta made another big mistake when it suddenly seized the Theban citadel in 383 and installed yet another puppet government. They now installed a government after the Athenian model as they knew that Thebes would not accept an oligarchy, but this attempt was so clumsy that it soon had turned against Sparta. The citadel was liberated again in 379 with the help of Athens, but Thebes was determined to get revenge while the rest of Hellas had even more reasons to doubt Sparta's role as guarantor of the King's peace. Thebes was even more humiliated by this peace as it had to give up its dominance over the other cities in Boeotia just to please Sparta.
Athens founded her second Athenian Naval Confedarcy in 378. The official goal of this second Delian League was a democratic freedom-fight against the Spartan oppressor. It was more likely that Athens simply used the anti-Sparta attitude in the hope of reviving her once formidable empire. The democratic coalition seemed to have lost all its justification when Thebes reclaimed its leadership of Boeotia by reviving the Boeotian League.
Thebes also started to rebuild its army after the Spartan government had been liquidated, and the Spartan garrisson had been defeated. Remarkable was that the Theban army only consisted of citizens at the first stage of the Theban hegemony, while the rest of the ancient world became more and more dependant of mercenaries. This was also the time that the famous elite corps of Thebes was founded by Gorgidas: the devoted brothers in arms. Traditionally this corps consisted of 150 homosexual male couples. You should realise that there was nothing perverse about homosexuality in the Greek world, unlike as in many other ancient civilizations. Homer had already mentioned in the Illiad that such a unit could be very useful, and Plato mentions it also as the men would try to compete with their partners in bravery, but they would also be determined to protect their partners.
In Thebes two strong men had come to the front: Pelopidas and Epaminondas. Especially Epaminondas was a brilliant leader and general who was a very flexible person in a rapidly changing world of warfare. The Spartan army was commandd by one of its two kings: Cleombrotos.
The Spartans marched into Boeotia under the command of their king Cleombrotos and stopped at Leuctra, not far from Thebes. Epaminondas knew that his army was severly outnumbered, but realised that he had to face the Spartans nevertheless. He managed to convince his men that an open battle was their only hope and together with their elite unit 'the Devoted Brothers in Arms', under the leadership of Pelopidas, they entered the plains. Cleombrotos placed his army in a half-moon 12 men deep phalanx , with peltasts covering both sides of the phalanx. Epaminondas had completly different ideas. His strategy was based on two principles.
The first principle that a direct fight between two phalanxes could end up in two different ways of fighting. The hoplites could attack eachother with their spears, or they could end up with their shields pressed against eachother. Two completly different ways with the same result: the phalanx that would loose its formation would become an easy target and would most likely loose the battle. When the hoplites ended up with their shields against eachother the battle looked a bit like a rugby match: the side who could press the hardest would break the enemy formation. Epaminondas realised that he could gain an advantage with a deeper phalanx. For the Spartans this tactic was new as they always relied on their spears, but the Thebans had already defeated Athens at Delium with a phalanx of 25 men deep.
The second principle was that one of the main problems of the phalanx had been to keep it going straight forward. It always tended to curl to the right, as the hoplite instinctive moved to the right to gain more protection from the shield of the hoplite beside them. Epimondas used a sloped phalanx with the strong left wing moved forwards. The left wing would destroy the right wing of the enemy, which traditionally consisted of the strongest and most experienced fighters, creating confusion among the enemy and breaking open the right wing. Now the left wing could break through the formation and attack the rest of the hostile phalanx in the side or in the back while the rest of the friendly phalanx got close enough to attack the enemy.
Epaminondas thus placed his army in the formation of a sloped phalanx. The left side of his phalanx was 50 men deep, but because of this he did not have enough men left to form a right wing. Peltasts would cover the right side of his phalanx, while the cavalry and the 'Devoted Brothers in Arms' would protect the left side.
Cleombrotos finally realises Epaminondas' plans when the Theban phalanx moves in for the kill. He attempts to reinforce his right wing but the well timed charge of the 'Devoted Brothers in Arms', who form the front of the Theban left wing, leaves him no time for this. Confusion sets in among the Spartans when the Theban shields clashes onto theirs. Cleombrotos is killed in the first stage of the struggle and the confusion among Sparta and its allies becomes even bigger when the weight of the Theban phalanx pushes the Sparta phalanx back.
The results of the battle.
With the destruction of the Spartan power at the battle of Leuctra the decade of Theban hegemony had begun. Leuctra was a defeat for Sparta, but it was not this military defeat which resulted in the end of Sparta. Thebes undertook several offensive actions in the Peloponese during its leadership of Hellas. This resulted in the founding of an Arcadian League under the leadership of the new found city of Megalopolis. Most important however was that Thebes refounded Messenia as an independent state in 369 after many years of helotage. Sparta sank to second-class among the Greek Poleis, and this allowed Thebes and Athens to pursue their rivalry in the vacuum created by the sudden disappearance of Sparta.