Answer
Epaminondas's victory over Sparta at the Battle of Leuctra in 371 BCE shattered Sparta's military dominance. Epaminondas's innovative tactics, including the use of a deep phalanx and cavalry on the flanks, proved superior to Sparta's traditional hoplite formation. This defeat marked a turning point in Greek history, as it weakened Sparta's hold on power and paved the way for the rise of Thebes as a major force in Greece.