How did Thebes rise as a Greek power during the 4th century BCE?

Thebes rose as a dominant Greek power in the 4th century BCE primarily through the military and political leadership of Epaminondas and his colleague Pelopidas, following the liberation of the city from a Spartan garrison in 379 BCE.12

Military Innovation and Hegemony

Thebes reorganized the Boeotian League along democratic lines and challenged Spartan dominance through revolutionary military tactics. At the Battle of Leuctra in 371 BCE, Epaminondas abandoned traditional phalanx conventions by massing his troops on the left wing to a depth of 50 ranks, fronted by the elite Sacred Band. This crushing blow shattered the Spartan army, effectively ending Sparta's long-standing military supremacy.321

Political Expansion

Following Leuctra, Thebes exerted influence across Greece by:
* Invading the Peloponnese: Epaminondas led multiple expeditions that weakened Sparta by refounding Messene and supporting the creation of the Arcadian federation, which permanently crippled Sparta's economic and military base.14
* Promoting Federalism: Thebes encouraged the formation of federal states in central Greece and the Peloponnese, exporting the Boeotian model of governance.4
* Challenging Athens: Thebes contested Athenian naval power and influence in northern Greece, briefly establishing its own maritime presence in the Aegean.15

Thebes's period of prominence concluded after the Battle of Mantineia in 362 BCE, where the death of Epaminondas left the city without the leadership necessary to sustain its hegemony.15