Battle of Leuctra

The Spartan hegemony lasted another 16 years, until, when attempting to impose their will on the Thebans, the Spartans were defeated at Leuctra in 371 BC. The Theban general Epaminondas then led Theban troops into the Peloponnese, whereupon other city-states defected from the Spartan cause. The Thebans were thus able to march into Messenia and free the helot population.