Which battle in 371 BCE ended Sparta’s dominance in Greece?

The Battle of Leuctra in 371 BCE ended Sparta’s dominance in Greece.

At Leuctra in Boeotia, the Theban army led by Epaminondas defeated a Spartan-led force commanded by King Cleombrotus I. The victory shattered the military reputation and political supremacy Sparta had built after defeating Athens in the Peloponnesian War.

Epaminondas used an unusually deep concentration of troops on the Theban left and a refused right wing. This formation helped the Thebans strike the Spartan position with overwhelming force. Cleombrotus was killed, and many elite Spartan citizens fell.

The defeat opened the way for Theban intervention in the Peloponnese. Thebes invaded Spartan territory, and Messenia was liberated from Spartan control soon afterward. Sparta remained an important Greek state, but it never recovered its earlier dominance.